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      .   Contaminant Candidate
      \  List Regulatory
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         Document for Aldrin and
         Dieldrin
                            Printed on Recycled Paper

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           Contaminant Candidate List
   Regulatory Determination Support Document
             for Aldrin and Dieldrin
       U.S. Environmental Protection Agency
             Office of Water (4607M)
      Standards and Risk Management Division
              Washington, DC 20460

http://www.epa.gov/SAFEWATER/ccl/cclregdetermine.html
                 EPA-815-R-03-010
                     Jury 2003
                                                  Printed on Recycled Paper

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                              Disclaimer

This document is designed to provide supporting information regarding the
regulatory determinations for aldrin and dieldrin as part of the Contaminant
Candidate List (CCL) evaluation process.  This document is not a regulation, and
it does not substitute for the Safe Drinking Water Act (SDWA) or the
Environmental Protection Agency's (EPA s) regulations.  Thus, it cannot impose
legally-binding requirements on EPA, States, or the regulated community, and
may not apply to a particular situation based upon the circumstances. Mention
of trade names or commercial products does not constitute endorsement or
recommendation for use.

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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


                               ACKNOWLEDGMENTS

   This document was prepared in support of the EPA Office of Ground Water and Drinking
Water's regulatory determinations for aldrin and dieldrin as part of the Contaminant Candidate
List (CCL) evaluation process.  Karen Wirth and Tom Carpenter served as EPA's Co-Team
Leaders for the CCL regulatory determination process and Ephraim King as Standards and Risk
Management Division Director. Harriet Colbert served as Work Assignment Manager. The
CCL Work Group provided technical guidance throughout. In particular, Karen Wirth, Dan
Olson, and Joyce Donohue provided scientific and editorial guidance. External expert reviewers
and many stakeholders provided valuable advice to improve the CCL Program and this
document.  The Cadmus Group, Inc., served as the primary contractor providing support for this
work.  The major contributions of Matt Collins, Emily Brott,  Ashton Koo, Richard Zeroka, and
Brent Ranalli are gratefully acknowledged. George Hallberg served as Cadmus' Project
Manager.

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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


               USEPA, Office of Water Report: EPA 815-R-03-010, July 2003

                         CONTAMINANT CANDIDATE LIST
             REGULATORY DETERMINATION SUPPORT DOCUMENT
                            FOR ALDRIN AND DIELDRIN

                               EXECUTIVE SUMMARY
   Aldrin and dieldrin were 1998 Contaminant Candidate List (CCL) regulatory determination
priority contaminants. Aldrin and dieldrin were two of the contaminants considered by the US
Environmental Protection Agency (EPA) for a regulatory determination. The available data on
occurrence, exposure, and other risk considerations suggest that regulating aldrin and dieldrin
with a National Primary Drinking Water Regulation (NPDWR) may not present a meaningful
opportunity to reduce health risk. EPA presented preliminary CCL regulatory determinations
and further analysis in the June 3, 2002 Federal Register Notice (USEPA 2002a; 67 FR 38222)
and confirmed the final regulatory determinations in a July 18, 2003 Federal Register Notice
(USEPA 2003a; 68 FR 42898).

   To make this regulatory determination for aldrin and dieldrin, EPA used approaches guided
by the National Drinking Water Advisory Council's (NDWAC) Working Group on CCL and
Six-Year Review. The Safe Drinking Water Act (SDWA) requirements for National Primary
Drinking Water Regulation (NPDWR) promulgation guided protocol development.  The SDWA
Section 1412(b)(l)(A) specifies that the determination to regulate a contaminant must be based
on a finding that each of the following criteria are met: (i)  "the contaminant may have adverse
effects on the health of persons"; (ii) "the contaminant is known to occur or there is substantial
likelihood that the contaminant will occur in public water systems with  a frequency and at levels
of public health concern"; and (iii)  "in the sole judgement  of the Administrator, regulation of
such contaminant presents a meaningful opportunity for health risk reduction for persons served
by public water systems."  Available data were evaluated to address each of the three statutory
criteria.

   Aldrin and dieldrin, related synthetic organic compounds (SOCs), are insecticides that were
discontinued for most agricultural uses in 1974 and all uses in 1987. They were used primarily
on corn and citrus products, as well as for general crops and timber preservation.  In addition,
aldrin and dieldrin were used for termite-proofing plywood, building boards, and the plastic and
rubber coverings of electrical and telecommunication cables.  Aldrin is considered moderately
persistent in the environment, with a half-life of approximately 110 days.  Dieldrin is among the
common degradates of aldrin.  Dieldrin is considered extremely persistent, with a half-life of up
to seven years.

   Aldrin and dieldrin were monitored from 1993 to 1999 under the SDWA Unregulated
Contaminant Monitoring (UCM) program. Aldrin and dieldrin are also regulated or monitored
by other federal programs including the Clean Water Act Priority Pollutants list, the
Comprehensive Environmental Response, Compensation,  and Liability Act (CERCLA), and the
Resource Conservation and Recovery Act (RCRA). In addition, the Emergency Planning and
Community Right-to-Know Act (EPCRA) has listed aldrin as an extremely hazardous substance
(EHS) and aldrin is on EPCRA's Toxic Release Inventory (TRI).

   Aldrin and dieldrin have been detected at low frequencies and concentrations in ambient
surface and ground water and stream bed sediments sampled by the United States Geological
Survey's (USGS) National Water Quality Assessment (NAWQA) program.  Dieldrin's
occurrence is greater in stream bed sediments and biotic tissue.  TRI data suggest that aldrin
continues to be released to the environment in small quantities even though it is no longer

                                           iii

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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


produced or used commercially in the United States. The presence and persistence of aldrin and
dieldrin in the environment is also evidenced by detections at National Priorities List (NPL)
hazardous waste sites in at least 31 States  and 38 States for aldrin and dieldrin, respectively, and
detections in site samples in at least 40 States (both substances) recorded in the Agency for
Toxic Substances and Disease Registry's (ATSDR) Hazardous Substance Release and Health
Effects Database (HazDat).

    Aldrin and dieldrin have also been detected in public water system (PWS) samples collected
under SDWA. Occurrence estimates from a cross-section of States with UCM data are very low
with only 0.006% and 0.06% of all samples showing detections for aldrin and dieldrin,
respectively. Systems with detections of aldrin and dieldrin constitute approximately 0.02% and
0.1% of cross-section systems respectively.  Systems with detections above the Health Reference
Level (HRL) of 0.002 |ig/L, a preliminary health effect level used for this analysis, are also
estimated at 0.02% and 0.1% of cross-section systems, because the HRL for aldrin and dieldrin
is lower than the Minimum Reporting Level (MRL). National estimates for the population
served by PWSs with simple detections (> MRL) and detections above the HRL are also very
low, about 40,000 people (roughly 0.02% of the population served by PWSs) for aldrin, and
150,000 people (0.1% of the population) for dieldrin.  Using more conservative estimates of
occurrence from all States reporting SDWA monitoring data,  including States with biased data,
0.2% of the nation's PWSs and 0.5% of the PWS population served (approximately 1,052,000
people) may have aldrin detections > MRL and > HRL, and 0.2% of the nation's PWSs and
0.4% of the PWS population served (approximately 793,000 people) may have comparable
detections of dieldrin. Additional SDWA compliance data from the corn belt States of Iowa,
Indiana, and Illinois, examined through independent analyses, support the drinking water data
analyzed in this report. Surface water detections were low in Indiana and Illinois PWSs,
comparable with data obtained through the cross-section  model.  No detections were reported in
the state of Iowa, or in Illinois and Indiana PWS groundwater.

    The available toxicological data indicate that aldrin and dieldrin have the potential to cause
adverse health effects in humans  and animals. In humans, acute aldrin/dieldrin toxicity is most
commonly manifested in the central nervous system as hyperirritability, convulsions and coma,
in some cases followed by cardiovascular effects such as unusually rapid beating of the heart and
elevated blood pressure. In smaller doses over time, aldrin and dieldrin may cause headache,
dizziness, general malaise, nausea, vomiting and muscle twitching, or muscle spasms.  Aldrin
and dieldrin toxicity may also be responsible for reported cases of immunohemolytic and aplastic
anemia. Aldrin and dieldrin appear to be weak endocrine disrupters, affecting the reproductive
system of animal subjects.  Though their carcinogenicity  in mice is established, no occupational
or epidemiological study has convincingly linked aldrin or dieldrin to cancer in humans.

    While there is evidence that aldrin and dieldrin have adverse health effects in humans, their
occurrence in drinking water at frequencies or concentrations significant for public health
concern is low. Furthermore, occurrence of aldrin and dieldrin in drinking water supplies in the
coming years is likely to decrease, since the substances are no longer commercially produced or
used. Therefore regulation of aldrin and dieldrin may be unlikely to represent a meaningful
opportunity for health risk reduction.
                                            IV

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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


                               TABLE OF CONTENTS

ACKNOWLEDGMENTS	i

EXECUTIVE SUMMARY	iii

TABLE OF CONTENTS	v

LIST OF TABLES	  vii

LIST OF FIGURES	ix

1.0  INTRODUCTION	1
    1.1 Purpose and Scope 	1
    1.2 Statutory Framework/Background	1
    1.3 Statutory History of Aldrin and Dieldrin  	2
    1.4 Regulatory Determination Process	3
    1.5 Determination Outcome  	4

2.0 CONTAMINANT DEFINITION	4
    2.1 Physical and Chemical Properties	4
    2.2 Environmental Fate/Behavior	5

3.0 OCCURRENCE AND EXPOSURE 	6
    3.1 Use and Environmental Release	7
       3.1.1  Production and Use  	7
       3.1.2 Environmental Release  	7
    3.2 Ambient Occurrence	8
       3.2.1  Data Sources and Methods 	8
       3.2.2 Results 	9
          3.2.2.1 Aldrin 	9
          3.2.2.2 Dieldrin	10
    3.3 Drinking Water Occurrence  	11
       3.3.1  Analytical Approach  	13
          3.3.1.1 UCM Rounds 1 and 2	13
          3.3.1.2 Developing a Nationally Representative Perspective	14
             3.3.1.2.1 Cross-Section Development  	14
             3.3.1.2.2 Cross-Section Evaluation	15
          3.3.1.3 Data Management and Analysis	16
          3.3.1.4 Occurrence Analysis	17
          3.3.1.5 Additional Drinking Water Data from the Corn Belt	19
       3.3.2 Results 	20
          3.3.2.1 Aldrin 	20
             3.3.2.1.1 Occurrence Estimates 	20
             3.3.2.1.2 Regional Patterns	24
          3.3.2.2 Dieldrin	24
             3.3.2.2.1 Occurrence Estimates 	24
                 3.3.2.2.2 Regional Patterns	25
    3.4 Conclusion  	25

4.0 HEALTH  EFFECTS 	26
    4.1 Hazard Characterization and Mode of Action Implications	26
    4.2 Dose-Response Characterization and Implications in Risk Assessment  	31
    4.3 Relative Source Contribution	32

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   4.4 Sensitive Populations 	33
   4.5 Exposure and Risk Information 	33
   4.6 Conclusion  	34

5.0 TECHNOLOGY ASSESSMENT	34
   5.1 Analytical Methods	34
   5.2 Treatment Technology 	34

6.0 SUMMARY AND CONCLUSIONS - DETERMINATION OUTCOME  	36

REFERENCES 	39

APPENDIX A: Abbreviations and Acronyms	47
                                        VI

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Regulatory Determination Support Document for Aldrin and Dieldrin
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                                    LIST OF TABLES

Table 2-1:  Physical and chemical properties  	5
Table 3-1:  Aldrin detections in stream bed sediments	11
Table 3-2:  Dieldrin detections and concentrations in streams and ground water	12
Table 3-3:  Dieldrin detections and concentrations in sediments, whole fish, and bivalves
    (all sites)	12
Table 3-4:  Summary occurrence statistics for aldrin  	21
Table 3-5:  Summary occurrence statistics for dieldrin	27
Table 5-1:  Analytical methods for aldrin and dieldrin	35
                                            vn

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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


                                   LIST OF FIGURES

Figure 3-1: Geographic distribution of cross-section States for Round 2 (SDWIS/FED)	16
Figure 3-2: States with PWSs with detections of aldrin for all States with data in SDWIS/FED
    (Round 2)	22
Figure 3-3: Round 2 cross-section States with PWSs with detections of aldrin (any PWSs with
    results greater than the Minimum Reporting Level [MRL]; above) and concentrations greater
    than the Health Reference Level (HRL; below)  	23
Figure 3-4: States with PWSs with detections of dieldrin for all States with data in SDWIS/FED
    (Round 2)	28
Figure 3-5: Round 2 cross-section States with PWSs with detections of dieldrin (any PWSs with
    results greater than the Minimum Reporting Level [MRL]; above) and concentrations greater
    than the Health Reference Level (HRL; below)  	29
                                           IX

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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


1.0  INTRODUCTION

1.1 Purpose and Scope

    This document presents scientific data and summaries of technical information prepared for,
and used in, the Environmental Protection Agency's (EPA) regulatory determinations for aldrin
and dieldrin. Information regarding the physical and chemical properties, environmental fate,
occurrence and exposure, and health effects of aldrin and dieldrin is included. Analytical
methods and treatment technologies are also discussed.  Furthermore, the regulatory
determination process is described to provide the rationale for the decision.

1.2 Statutory Framework/Background

    The Safe Drinking Water Act (SDWA), as amended in 1996, requires the EPA to publish a
list of contaminants (referred to as the Contaminant Candidate List, or CCL) to assist in priority-
setting efforts. The contaminants included on the CCL were not subject to any current or
proposed National Primary Drinking Water Regulations (NPDWR), were known or anticipated
to occur in public water systems, and were known or suspected to adversely affect public health.
These contaminants therefore may require regulation under SDWA. The first Drinking Water
CCL was published on March 2, 1998 (USEPA, 1998a;  63 FR 10274), and a new CCL must be
published every five years thereafter.

    The 1998 CCL contains 60  contaminants, including  50 chemicals or chemical groups, and 10
microbiological contaminants or microbial groups.  The SDWA also requires the Agency to
select 5 or more contaminants from the current CCL and determine whether or not to regulate
these contaminants with an NPDWR.  Regulatory determinations for at least 5 contaminants
must be completed 3!/2 years after each new CCL.

    Language in SDWA Section 1412(b)(l)(A) specifies that the determination to regulate a
contaminant must be based on a finding that each of the following criteria are met:

    Statutory Finding i.   the contaminant may have adverse effects on the health of persons;

    Statutory Finding ii.   the contaminant is known to occur or there is substantial likelihood
       that the contaminant will occur in public water systems with a frequency and at levels of
       public health concern; and

    Statutory Finding Hi.  in the sole judgement of the Administrator, regulation of such
       contaminant presents a meaningful opportunity for health risk reduction for persons
       served by public water systems.

    The geographic distribution of the contaminant is another factor evaluated to determine
whether it occurs at the national, regional or local level. This consideration is important because
the Agency is charged with developing national regulations and it may not be appropriate to
develop NPDWRs for regional  or local contamination problems.

    EPA must determine if regulating this CCL contaminant will present a meaningful
opportunity to reduce health risk based on contaminant occurrence, exposure, and other risk
considerations. The Office of Ground Water and Drinking Water (OGWDW) is charged with
gathering and analyzing the occurrence, exposure, and risk information necessary to support this
regulatory decision.  The OGWDW must evaluate when and where this contaminant occurs, and
what would be the exposure and risk to public health. EPA must evaluate the impact of potential
regulations as well as determine the appropriate measure(s) for protecting public health.

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   For each of the regulatory determinations, EPA first publishes in the Federal Register the
draft determinations for public comment.  EPA responds to the public comments received, and
then finalizes the regulatory determinations.  If the Agency finds that regulations are warranted,
the regulations must then be formally proposed within 24 months, and promulgated 18 months
later.  EPA has determined that there is sufficient information to support regulatory
determinations for aldrin and dieldrin.

1.3 Statutory History of Aldrin and Dieldrin

   Aldrin and dieldrin have been monitored under the SDWA Unregulated Contaminant
Monitoring (UCM) program since 1993 (USEPA, 1992; 57 FR 31776). Monitoring ceased for
small public water systems (PWSs) under a direct final rule published January 8, 1999 (USEPA,
1999a; 64 FR 1494), and ended for large PWSs with promulgation of the new Unregulated
Contaminant Monitoring Regulation (UCMR) issued September 17, 1999 (USEPA, 1999b; 64
FR 50556) and effective January 1, 2001. At the time the UCMR lists were developed, the
Agency concluded there were adequate monitoring data for regulatory determinations. This
obviated the need for continued monitoring under the new UCMR list.

   EPA previously recommended guidelines for exposure to aldrin and dieldrin in drinking
water through health advisories issued in 1991 and 1988, respectively (USEPA, 199la; USEPA,
1988). As part of the CCL process,  health effects data have been reviewed. These are
summarized in section 4.0 of this document.

   Aldrin and dieldrin are regulated or monitored by other federal programs as well.  They are
included on the Clean Water Act Priority Pollutants list for which the EPA establishes ambient
water quality criteria.  The Comprehensive Environmental Response, Compensation, and
Liability Act (CERCLA or "Superfund") includes aldrin and dieldrin as hazardous substances
while the Resource Conservation and Recovery Act (RCRA) classifies them as hazardous
constituents (USEPA, 2000e).  CERCLA's listing requires reporting of releases over a certain
"reportable quantity" which, for aldrin and dieldrin, is one pound (USEPA, 1996).

   In addition, the Emergency Planning and Community Right-to-Know Act (EPCRA) has
listed aldrin as an extremely hazardous substance (EHS).  The presence of EHSs in excess of the
Threshold Planning Quantity (TPQ), requires certain emergency planning activities to be
conducted.  For aldrin, the  Threshold Planning Quantity is 500 Ibs if it is in molten form, in
solution, or in powder  form with particle size less than 100 microns.  Otherwise, aldrin's TPQ is
10,000 Ibs (USEPA, 1996). Aldrin is also on EPCRA's Toxic Release Inventory (TRI). The
TRI requires certain industrial sectors to publicly report the environmental release or transfer of
listed chemicals (USEPA, 2000c).

   The Occupational Safety and Health Administration (OSHA) recommends occupational
exposure limits for aldrin and dieldrin of 250 |ig/m3 for an 8-hour workday over a  40-hour
workweek.  The National Institute for Occupational Safety and Health (NIOSH) suggests that
aldrin and dieldrin levels be kept at the lowest amounts that can be measured reliably  (ATSDR,
1993).

   The U.S. Department of Agriculture (USD A) discontinued registration and use of aldrin and
dieldrin as pesticides in 1970. In 1972, EPA canceled all but the following three uses of aldrin
and dieldrin: subsurface ground insertion for termite control, the dipping of nonfood plant roots
and tops, and moth-proofing in manufacturing processes using completely closed systems.  This
cancellation decision was finalized in 1974. The sole manufacturer of aldrin and dieldrin, Shell
Chemical Company, ceased producing the compounds for moth-proofing and the dipping of non-
food plants in 1974, and canceled their use as termiticides in  1987 (ATSDR, 1993).

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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


1.4 Regulatory Determination Process

   In developing a process for the regulatory determinations, EPA sought input from experts
and stakeholders.  EPA asked the National Research Council (NRC) for assistance in developing
a scientifically sound approach for deciding whether or not to regulate contaminants on the
current and future CCLs.  The NRC's Committee on Drinking Water Contaminants
recommended that EPA: (1) gather and analyze health effects, exposure, treatment, and
analytical methods data for each contaminant; (2) conduct a preliminary risk assessment for each
contaminant based on the available data; and (3) issue a decision document for each contaminant
describing the outcome of the preliminary risk assessment. The NRC noted that in using this
decision framework, EPA should keep in mind the importance of involving all interested parties.

   One of the formal means by which EPA works with its stakeholders is through the National
Drinking Water Advisory Council (NDWAC). The NDWAC comprises members of the general
public, State and local agencies, and private groups concerned with safe drinking water, and
advises the EPA Administrator on key aspects of the Agency's drinking water program. The
NDWAC provided specific recommendations to EPA on a protocol to assist the Agency in
making regulatory determinations for current and future CCL contaminants.  Separate but similar
protocols were developed for chemical and microbial contaminants. These protocols are
intended to provide a consistent approach to evaluating contaminants for regulatory
determination, and to be a tool that will  organize information in a manner that will communicate
the rationale for each determination to stakeholders.  The possible outcomes of the regulatory
determination process are: a decision to regulate, a decision not to regulate, or a decision that
some other action is needed (e.g., issuance of guidance).

   The NDWAC protocol uses the three statutory requirements of SDWA Section
1412(b)(l)(A)(i)-(iii) (specified in section 1.2) as the foundation for guiding EPA in making
regulatory determination decisions.  For each statutory requirement, evaluation criteria were
developed and are summarized below.

   To address whether a  contaminant may have adverse effects on the health of persons
(statutory requirement (i)), the NDWAC recommended that EPA characterize the health risk and
estimate a health reference level for evaluating the occurrence data for each contaminant.

   Regarding whether a contaminant is known to  occur, or whether there is substantial
likelihood that the contaminant will occur, in public water systems with a frequency, and at
levels, of public health concern (statutory requirement (ii)), the NDWAC recommended that
EPA consider: (1) the actual and estimated national percent  of public water systems (PWSs)
reporting detections above half the health reference level; (2) the actual and estimated national
percent of PWSs with detections above the health reference  level; and (3) the geographic
distribution of the contaminant.

   To address whether regulation of a contaminant presents a meaningful opportunity for health
risk reduction for persons served by public water systems (statutory requirement (iii)) the
NDWAC recommended that EPA consider estimating the national population exposed above
half the health reference level and the national population exposed above the health reference
level.

   The approach EPA used to make regulatory determinations followed the general format
recommended by the NRC and the NDWAC to satisfy the three SDWA requirements under
Section 1412(b)(l)(A)(i)-(iii).  The process was independent of many of the more detailed and
comprehensive risk management factors that will influence the ultimate regulatory decision
making process.  Thus, a decision to regulate is the beginning of the Agency regulatory
development process, not the end.

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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


    Specifically, EPA characterized the human health effects that may result from exposure to a
contaminant found in drinking water. Based on this characterization, the Agency estimated a
health reference level (HRL) for each contaminant.

    For each contaminant EPA estimated the number of PWSs with detections >/^HRL and
>HRL, the population served at these benchmark values,  and the geographic distribution, using a
large number of occurrence data (approximately seven million analytical points) that broadly
reflect national  coverage. Round 1 and Round 2 UCM data, evaluated for quality, completeness,
bias, and representativeness, were the primary data used to develop national occurrence
estimates. Use  and environmental release information, additional drinking water data sets (e.g.,
State drinking water data sets, EPA National Pesticide Survey, and Environmental Working
Group data reviews), and ambient water quality data (e.g., NAWQA, State and regional studies,
and the EPA Pesticides in Ground Water Database) were also consulted.

    The findings from these evaluations were used to determine if there was adequate
information to evaluate the three SDWA statutory requirements and to make a determination of
whether to regulate a contaminant.

1.5 Determination Outcome

    After reviewing the best available public health and occurrence information, EPA has made a
determination not to regulate the contaminants aldrin and dieldrin with NPDWRs. EPA has
found that aldrin and dieldrin may have adverse effects on the health of persons and are known
to occur in at least some  PWSs. However, EPA has not found that they occur in public water
systems at frequencies or levels of public health concern. Furthermore, all uses of these
compounds were suspended in 1987. EPA does not consider exposure to aldrin or dieldrin to be
widespread nationally. All CCL regulatory determinations are formally presented in the Federal
Register Notices (USEPA, 2002a; 67 FR 38222; and USEPA, 2003a; 68 FR 42898). The
following sections summarize the data used by the Agency to reach this decision.


2.0 CONTAMINANT DEFINITION

    Aldrin and dieldrin are both synthetic organic compounds (SOCs) that are white powders
when pure, but tan powders in their technical-grade forms. Aldrin is generated by the Diels-
Alder condensation of hexachlorocyclopentadiene with bicyclo[2.2.1]-2,5-heptadiene.  Its
chemical name  is  l,2,3,4,10,10-hexachloro-l,4,4oc,5,8,8oc-hexahydro-l,4-endo,exo-5,8-
dimethanonaphthalene (abbreviated HHDN).  Dieldrin is generated by the epoxidation of aldrin.
The chemical name for dieldrin is 1,2,3,4,10,10-hexachloro-6,7-epoxy-l,4,4a,5,6,7,8,8a-
octahydro-l,4-endo,exo-5,8-dimethanonaphthalene (abbreviated HEOD).  The Shell Chemical
Company was the sole United States manufacturer and distributor of these compounds. Trade
names for aldrin include: Aldrec, Aldrex, Drinox, Octalene, Seedrin, and Compound 118.  Some
dieldrin trade names are: Alvit, Dieldrix, Octal ox, Quintox, and Red Shield (ATSDR, 1993).
Aldrin and dieldrin are insecticides that were discontinued for all uses in 1987.  Aldrin  and
dieldrin combat insects by contact or ingestion, and were used primarily on corn and citrus
products, as well as for general crops and timber preservation. In addition, aldrin and dieldrin
were used for termite-proofing plywood, building boards, and the plastic and rubber coverings of
electrical and telecommunication cables (ATSDR, 1993).

2.1 Physical and Chemical Properties

    Table 2-1 lists summary information regarding the physical  and chemical properties of aldrin
and dieldrin.  Also included are their CAS Registry Numbers and molecular formulas.

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Regulatory Determination Support Document for Aldrin and Dieldrin
                                                                               July 2003
Table 2-1: Physical and chemical properties
Identification
// // ', * ^ ,--
CAS number
Molecular Formula
P/hfiieaJ/and
/ ftf$f jcaf Pro'prtif f
Boiling Point
Melting Point
Molecular Weight
Log Koc
Log Kow
Water Solubility
Vapor Pressure
Henry's Law Constant
^Aldrin
309-00-2
Ci2H8Q6
^A||tein
145 C
104 C pure, 40-60 C technical
grade
364.93 g/mol
4.69
6.5*
0.20 mg/L at 25 C
1.4x 10-4mmHgat25C
1.30x ID'2
J^ieldfin
60-57-1
C12H8C160
Dieldrin
-W^
330 C
175-176 C pure, 95 C
technical grade
380.93 g/mol
3.87
4.55
0.1 8 mg/L at 25 C
7.78 x 10-7mmHgat25C
6.16x ID'4
after ATSDR, 1993; "Howard, 1991.
 note: this quantity is expressed in a
this quantity is expressed in a dimensionless form.
2.2 Environmental Fate/Behavior

    Aldrin readily converts to dieldrin in aerobic terrestrial and aqueous environments, as well as
in the atmosphere. Aldrin has a low leaching potential (or high soil/water partitioning) and does
not volatilize appreciably from subsurface soil particles (50% loss after 10-15 weeks). Its
volatilization is more rapid at the soil surface (50% loss after 1-2 weeks), causing significant loss
to the atmosphere post-application.  Dieldrin also does not volatilize readily from soil, although
volatilization is still an important loss process for this persistent compound. Dieldrin sorbs
strongly to soils and resists leaching to ground water systems, but can be present in run-off to
surface water, sorbed to waterborne sediments (ATSDR, 1993; Howard, 1991).  Laboratory
studies suggest that aldrin rapidly degrades in the atmosphere to photoaldrin, dieldrin, or
photodieldrin (ATSDR, 1993). Dieldrin is broken down by hydroxyl radicals in the atmosphere
with an estimated half life of one day.  Dieldrin is more stable to this degradation when attached
to particulate matter in the atmosphere, and can thus be transported long distances before it is
lost through wet or dry deposition. Due to this transport mechanism and to the compound's
resistance to abiotic degradation and biotransformation, dieldrin is persistent and widespread in
the environment (ATSDR,  1993; Howard, 1991).

    Aldrin is classified as a moderately persistent compound, which signifies that its half life in
soil ranges from 20-100 days (Howard, 1991). Aldrin degrades to dieldrin by epoxidation  in all
aerobic and biologically active soils. Another metabolite of aldrin in soil is aldrin acid (ATSDR,
1993).  Mathematical models estimate  that aldrin would degrade by 69% to dieldrin in 81 days

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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


when applied within 15 cm from the soil surface.  The half life of aldrin was estimated to be
approximately 110 days when applied to soil at a rate of 1.1-3.4 kg/hectare, with 95%
disappearance in 3 years.  The half life of aldrin was shown to be significantly lower in sandy
loam compared to clay loam soils (36.5 versus 97 days when applied at a rate of 9 kg/hectare;
ATSDR, 1993).

   Dieldrin is extremely persistent in soil, with a residence time of often greater than 7 years.
Although volatilization is dieldrin's most important terrestrial loss process, its low vapor
pressure keeps it from evaporating quickly from soil. Another loss process from soil is
adsorption on dust particles and atmospheric transport (Howard, 1991). An experiment with
dieldrin applied to a microagroecosystem demonstrated that 73% of the compound remained on
the soil surface after 11 days.  Soil moisture content also affects dieldrin volatilization rates.
One study showed that after five months, about 18% of dieldrin had volatilized from moist land
compared to 2% from flooded and 7% from dry lands (ATSDR, 1993). Volatilization rates for
dieldrin decrease with time and increase with increasing temperature to a maximum at 25C.
Dieldrin is highly resistant to biodegradation in soil, with an estimated half life in soil of 868
days (estimated using the Henry's law constant and the organic carbon partition coefficient, Koc;
ATSDR, 1993).

   Aldrin sorbs to soil and is not available to leach to ground water systems, as evidenced by its
general absence in ground water samples (ATSDR,  1993; Howard, 1991). However, small
amounts of aldrin have been detected in surface waters.  Volatilization is expected to be a
significant loss process for aldrin in water, with the rate of volatilization directly proportional to
wind speed and current velocity and inversely proportional to water body depth (Howard, 1991).
Aldrin was photooxidized by 75% to dieldrin following 48 hours of irradiation at 238 nm in
filtered natural field water.  Studies show that aldrin degrades under anaerobic conditions in
biologically active wastewater sludge (pH 7-8, 35 C) with a half life of under one week
(ATSDR, 1993).

   Dieldrin is also mostly absent from ground water samples because of its tendency to sorb to
soil. Dieldrin that is sorbed to waterborne sediments can run-off to surface waters. Dieldrin
does not undergo hydrolysis or significant aqueous biodegradation. Conflicting data exist
regarding the importance of volatilization for dieldrin in water (Howard,  1991; ATSDR, 1993).
Dieldrin is slowly converted in the presence of  sunlight to photodieldrin, a stereoisomer of the
compound (water half-life of 4 months; Howard, 1991). Dieldrin added to natural water (from a
drainage canal in an agricultural area) and incubated in the dark degraded by less than 20% in 16
weeks.  Dieldrin is stable against significant degradation in both biologically active and
anaerobic wastewater sludge (89% remained after 48 hours of continuous anaerobic digestion;
45% remained after 9 days of aerobic digestion; ATSDR, 1993).

   Aldrin and dieldrin have ranges of log Kow values from 5.68 to 7.4, and from 4.32 to 6.2,
respectively, suggesting high potentials for bioaccumulation. Dieldrin's extreme nonpolarity
gives it a strong affinity towards animal fat and plant waxes (ATSDR,  1993; Howard ,1991).


3.0 OCCURRENCE AND EXPOSURE

   This section examines the occurrence of aldrin and dieldrin in drinking water. While no
complete national database exists of unregulated or regulated contaminants in drinking water
from public water systems (PWSs) collected under the Safe Drinking Water Act (SOWA), this
report aggregates and analyzes existing State data that have been screened for quality,
completeness, and representativeness.  Populations served by PWSs exposed to aldrin and
dieldrin are estimated, and the occurrence data are examined for regional or other special trends.
To augment the incomplete national  drinking water data and aid in the evaluation of occurrence,

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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


information on the use and environmental release, as well as ambient occurrence of aldrin and
dieldrin, is also reviewed.

3.1 Use and Environmental Release

   3.1.1  Production and Use

   Aldrin and dieldrin combat insects by contact or ingestion, and were used primarily on corn
and citrus products, as well as for general crops and timber preservation. In addition, aldrin and
dieldrin were used for termite-proofing plywood, building boards, and the plastic and rubber
coverings of electrical and telecommunication cables (ATSDR, 1993).  In 1972, EPA canceled
all but the following three uses of aldrin and dieldrin: subsurface ground insertion for termite
control, the dipping of non-food plant roots and tops, and moth-proofing in manufacturing
processes using completely closed systems. This cancellation decision was finalized in 1974.

   Aldrin was not imported into the United States prior to the 1974 cancellation decision,
however  Shell International (Holland) imported the chemical for limited use from 1974 to 1985
(with the exception of 1979 and 1980, when imports were temporarily suspended). An estimated
1-1.5 million Ibs of aldrin were imported annually from 1981-1985,  after which time importation
ceased. No importation data were found for dieldrin. By 1987, all uses of aldrin and dieldrin
had been canceled voluntarily by the manufacturer (ATSDR, 1993).

   3.1.2  Environmental Release

   Aldrin is listed as a Toxic Release Inventory chemical.  In 1986, the Emergency Planning
and Community Right-to-Know Act (EPCRA) established the Toxic Release Inventory (TRI) of
hazardous chemicals. Created under the Superfund Amendments and Reauthorization Act
(SARA) of 1986, EPCRA is also sometimes known as  SARA Title III.  The EPCRA mandates
that larger facilities publicly report when TRI chemicals are released into the environment. This
public reporting is required for facilities with more than 10 full-time employees that annually
manufacture or produce more than 25,000 pounds, or use more than 10,000 pounds, of a TRI
chemical (USEPA, 1996; USEPA, 2000c).

   Under these conditions, facilities are required to report the pounds per year of aldrin released
into the environment both on- and off-site.  The production, import,  and use of aldrin had been
canceled  by the time the TRI was instated, however, and therefore no release or transfer data
were reported. In 1995, Resource Conservation and Recovery Act (RCRA) subtitle C hazardous
waste treatment and disposal facilities were added to the list of those facilities required to present
release data to the TRI.  This addition became effective for the 1998 reporting year, which is the
most recent TRI  data currently available. Waste treatment facilities  from three States (AR, MI,
TX) reported releases of aldrin in 1998, with on- and off-site releases totaling 25,622 pounds.
The on-site quantity is subdivided into air emissions, surface water discharges, underground
injections, and releases to land. Most of the aldrin released to the environment was released
directly to land (22,000 Ibs; USEPA, 2000a).

   Although the TRI data can be useful in giving a general idea of release trends, it is far from
exhaustive and has significant limitations.  For example, only industries that meet TRI criteria (at
least 10 full-time employees and the manufacture and processing of quantities exceeding 25,000
Ibs/yr, or use of more than 10,000 Ibs/yr) are required to report releases. These reporting criteria
do not account for releases from smaller industries. Also, the TRI data is meant to reflect
releases and should not be used to estimate general exposure to a chemical (USEPA, 2000b).

   Aldrin and dieldrin are included in the Agency for Toxic Substances and Disease Registry's
(ATSDR) Hazardous Substance Release and Health Effects Database (HazDat). This database

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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


records detections of listed chemicals in site samples; aldrin and dieldrin were both detected in
40 States. The National Priorities List (NPL) of hazardous waste sites, created in 1980 by the
Comprehensive Environmental Response, Compensation & Liability Act (CERCLA), is a listing
of some of the most health-threatening waste sites in the United States. Aldrin and dieldrin were
detected in NPL hazardous waste sites in 31 and 38 States, respectively (USEPA, 1999c).

   In summary, aldrin and dieldrin have not been produced in the United States since 1974, and
all uses of the pesticides were canceled by 1987. The chemicals had been used mostly on  corn
and citrus products. Aldrin was imported to the United States from Holland from 1974-1985
(with the exception of 1979 and 1980) in quantities of approximately 1-1.5 million Ibs/yr.  TRI
data from 1998  suggest that aldrin continues to be released into the environment, even though
the chemical is no longer produced nor used in the United States. The presence and persistence
of aldrin and dieldrin in the environment is evidenced by detections of the compounds in
hazardous waste sites in at least 31 and 38 States, respectively (at NPL sites), as well as
detections of both chemicals in site  samples in at least 40 States (listed in ATSDR's HazDat).

3.2 Ambient Occurrence

   To understand the presence of a chemical in the environment, an examination of ambient
occurrence is useful. In a drinking water context,  ambient water is source water existing in
surface waters and aquifers before treatment. The most comprehensive and nationally consistent
data describing  ambient water quality in the United States are being produced through the United
States Geological  Survey's (USGS) National Water Quality Assessment (NAWQA) program.
(NAWQA, however, is  a relatively young program and complete national data are not yet
available from their entire array of sites across the nation.)

   3.2.1  Data  Sources and Methods

   The USGS instituted the NAWQA program in 1991 to examine water quality status and
trends in the United States. NAWQA is designed  and implemented in such a manner as to allow
consistency and comparison between representative study basins located around the country,
facilitating interpretation of natural  and anthropogenic factors affecting water quality (Leahy and
Thompson, 1994).

   The NAWQA program consists of 59 significant watersheds and aquifers referred to as
"study units." The study units represent approximately two thirds of the overall water usage in
the United States and a  similar proportion of the population served by public water systems.
Approximately  one half of the nation's land area is represented (Leahy and Thompson, 1994).

   To facilitate management and make the program cost-effective, approximately one third  of
the study units at a time engage in intensive assessment for a period of 3 to 5 years. This is
followed by a period of less intensive research and monitoring that lasts between 5 and 7 years.
This way all 59 study units rotate through intensive assessment over a ten-year period (Leahy
and Thompson, 1994).  The first round of intensive monitoring (1991-96) targeted 20 units and
the second round monitored another 16 beginning in 1994. This first group was more heavily
slanted toward agricultural basins. A national synthesis of results from these study units,
focusing on pesticides and nutrients, has been compiled and analyzed (Kolpin et al., 2000;
Larson etal., 1999; USGS, 1999a).

   Aldrin was not an analyte for either the ground water or the surface water NAWQA studies
included in the pesticide and nutrient national synthesis (Kolpin et al., 1998; Larson et al., 1999;
USGS, 1999b).  Because of analytical and budget  constraints the NAWQA program targets
certain pesticides, many of which are high use and/or have potential environmental significance
(Larson et al., 1999; USGS, 1999a).  Aldrin may have been excluded because it breaks down in

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Regulatory Determination Support Document for Aldrin and Dieldrin                             July 2003


the environment to dieldrin (among other degradates), which is analyzed in the NAWQA studies
(USGS, 1999b). Aldrin persisting in the environment is more likely to be found in sediments or
biotic tissues because of its strong hydrophobicity and sorption potential (ATSDR, 1993;
Nowell, 1999; USGS, 2000). Consequently, NAWQA investigators focused their aldrin
occurrence studies on bed sediments and aquatic biota tissue (Nowell, 1999).

   Dieldrin is an analyte for both surface and ground water NAWQA studies.  Two of the first
20 study basins analyzed in the pesticide and nutrient national synthesis reports, the Central
Nebraska Basins and the White River Basin in Indiana, are located in the corn belt where
dieldrin use was heavy in the 1960s. The Minimum Reporting Level (MRL) for dieldrin is 0.001
|ig/L (Kolpin et al., 1998), substantially lower than most drinking water monitoring.

   Data are also available for dieldrin occurrence in surface water in the Mississippi River and
six major tributaries draining corn belt States (Goolsby and Battaglin, 1993). These data are the
result of a USGS regional water quality  investigation, and details regarding sampling and
analytical methods are described in the report.

   Aldrin and dieldrin are organochlorine insecticides. As a group, organochlorines are
hydrophobic and resist degradation.  Hydrophobic ("water hating") compounds have low water
solubilities and strong tendencies to sorb to organic material  in sediments and accumulate in the
tissue of aquatic biota, where they can persist for long periods of time (ATSDR, 1993; USGS,
2000). Organochlorines may be present in bed sediments and tissues of aquatic systems even
when they are undetectable in the water column using conventional methods (Nowell,  1999).
The occurrence of a toxic compound in  stream sediments is pertinent to drinking water concerns
because some desorption of the compound from sediments into water will occur through
equilibrium reactions, although in very low concentrations.

   To determine their presence in hydrologic systems of the United States, the NAWQA
program has investigated organochlorine pesticide detections in bed sediments and biotic tissue,
focusing on the organochlorine insecticides that were used heavily in the past (Nowell, 1999).
The occurrence of aldrin, one of the top three insecticides used for agriculture in the 1960s and
widely used to kill termites in structures until the mid 1980s, and dieldrin was investigated in
this study (Nowell, 1999; USGS, 1999a). Sampling was conducted at 591 sites from 1992-1995
in the 20 NAWQA study units where the first round of intensive assessment took place.  Two of
these basins, the Central Nebraska Basins and the White River Basin in Indiana, are located in
the corn belt where aldrin use was heavy in the 1960s. Details regarding sampling techniques
and analytical methods are described by Nowell (1999).

   3.2.2 Results

   3.2.2.1 Aldrin

   Aldrin was not detected in aquatic biota tissue samples. However, it was detected in stream
bed sediment samples.  The occurrence  frequencies above the Minimum Reporting Level (MRL)
of 1 |ig/kg, and basic summary statistics, indicate that occurrence in sediments is very  low
(Table 3-1). Both the median and 95th percentile concentrations were reported as non-detections
(< MRL) across all land use categories.

   Aldrin was detected in sediments only at agricultural or mixed land use sites, perhaps
reflecting the heavy agricultural use in the late 1960s and early 1970s (Table 3-1).  Interesting in
light of the more recent termiticide use,  no urban detections were reported.  This may be partly a
function of the NAWQA sampling design that targeted basins more representative of agricultural
and mixed land use conditions for the first round of intensive monitoring from which these

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Regulatory Determination Support Document for Aldrin and Dieldrin                             July 2003


sediment data were produced (see section 3.2.1 above) (Data from later rounds are not yet
available)

    3.2.2.2 Dieldrin

    Detection frequencies and concentrations of dieldrin in ambient surface and ground water are
low, especially in ground water which is the case for insecticides in general (Table 3-2; Kolpin et
al., 1998; Miller and Wilber, 1999). However, using a common reporting limit of 0.01 |ig/L,
dieldrin is the most commonly detected insecticide in ground water in these USGS studies. This
possibly reflects the historically heavy use of aldrin and dieldrin and clearly indicates dieldrin's
environmental persistence (Kolpin et al., 1998; Miller, 2000).  Also, though relatively immobile
in water when compared to newer pesticides, dieldrin is one of the most mobile of the older
organochlorine pesticides (USGS, 1999a).

    Dieldrin detection frequencies are considerably higher in shallow ground water in urban
areas as compared to shallow ground water in agricultural areas (Table 3-2), a likely
consequence of the more recent use of aldrin and dieldrin as a termiticide and industrial moth-
proofing agent until the mid-1980s. Agricultural uses were discontinued in the 1970s. Major
aquifers, which are generally deep, have very low detection frequencies and concentrations of
dieldrin. Hydrophobic compounds have high sorption  potential and are not very mobile in
ground water, making their occurrence in deep aquifers unlikely.

    In streams, detection frequencies  are higher compared to ground water (Table 3-2).
Dieldrin's chemical characteristics, chiefly its hydrophobicity, make it less likely to be
transported to the subsurface with ground water recharge. Instead, dieldrin sorbs easily to
sediments and biotic tissues and may persist in surface water environments for many years after
applications have ceased. Differences in detection frequencies and concentrations between
urban and agricultural settings are less pronounced for streams than for ground water, but
frequencies and concentrations are greater for streams  in agricultural  settings.

    The concentrations and detection frequencies of dieldrin in bed sediments and biotic tissues
are considerably higher than water, although the median concentration of all samples is still
below the MRL (Table 3-3). Occurrence of dieldrin is highest in whole fish, highlighting the
potential for it to bioaccumulate (Kolpin et al., 1998).  The trend of higher concentrations and
detection frequencies in urban environments is again apparent when examining dieldrin
occurrence across various land use settings in  sediments and biotic tissues.  Urban areas have the
highest detections  and concentrations. Occurrence in agricultural and mixed land use types is
lower and approximately equivalent.  Forest and rangeland show very low occurrence (Nowell,
1999).

    While concentrations in water are generally low, a  risk-specific dose (RSD) criteria of 0.02
|ig/L, a concentration associated with a cancer risk level of 1 in 100,000 people, was exceeded  at
one site at least, in both surface and ground water (Kolpin et al., 1998; Larson et al., 1999;
USGS, 1998).

    A USGS regional water quality investigation  provides additional information on the
occurrence of dieldrin in the corn belt. For surface water sampling from April  1991 to March
1992 from the Mississippi River and  six tributaries draining the corn belt, 8% of all samples and
71% of sites had detections greater than the reporting limit of 0.02 |ig/L.  The maximum
concentration was  approximately 0.03 |ig/L (Goolsby and Battaglin, 1993).
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Regulatory Determination Support Document for Aldrin and Dieldrin
                                                    July 2003
Table 3-1: Aldrin detections in stream bed sediments
                       Detection frequency
                   (% samples > MRL of 1 Jig/kg)
                             Concentration
                      (all samples; fig/kg dry weight)

urban
mixed
agricultural
forest-range land

0.0 %
0.5 %
0.6 %
0.0 %
median
nd*
nd
nd
nd
95th
percentile
nd
nd
nd
nd
maximum
nd
o
J
2.2
nd
     all sites
0.4 %
nd
nd
after Now ell, 1999
*not detected in concentration greater than MRL
3.3 Drinking Water Occurrence

    The SDWA, as amended in 1986, required public water systems (PWSs) to monitor for
specified "unregulated" contaminants, on a five year cycle, and to report the monitoring results
to the States. Unregulated contaminants do not have an established or proposed NPDWR, but
they are contaminants that were formally listed and required for monitoring under federal
regulations. The intent was to gather scientific information on the occurrence of these
contaminants to enable a decision as to whether or not regulations were needed.  All non-
purchased community water systems (CWSs) and non-purchased non-transient non-community
water systems (NTNCWSs), with greater than 150 service connections, were required to conduct
this unregulated contaminant monitoring. Smaller systems were not required to conduct this
monitoring under federal regulations, but were required to be available to monitor if the State
decided such monitoring was necessary.  Many States collected  data from smaller systems.
Additional contaminants were added to the Unregulated Contaminant Monitoring (UCM)
program in 1991 (USEPA, 1991b; 56 FR 3526) for required monitoring that began in 1993
(USEPA, 1992; 57 FR 31776).
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Regulatory Determination Support Document for Aldrin and Dieldrin
                                            July 2003
Table 3-2:  Dieldrin detections and concentrations in streams and ground water
                               Detection frequency
                              (% samples > MRL*)
                    Concentration percentiles
                       (all samples; fig/L)
streams
urban
integrator
agricultural
all sites
ground water
shallow urban
shallow
agricultural
major aquifers
all sites
%> 0.001 us/L

3.67%
3.27 %
6.90 %
4.64 %

5.65 %
0.97 %
0.43 %
1.42 %
%> 0.01 us/L

1.83 %
1.63 %
3.90%
2.39 %

3.32%
0.65 %
0.21 %
0.93 %
median
nd**
nd
nd
nd

nd
nd
nd
nd
95th

nd
nd
0.007
nd

0.005
nd
nd
nd
maximum
0.016
0.015
0.027
0.19

0.068
0.057
0.03
0.068
after USGS, 1998
*MRLfor dieldrin in water studies: 0.001 [ig/L.
* *not detected in concentrations greater than MRL
Table 3-3:  Dieldrin detections and concentrations in sediments, whole fish, and bivalves
(all sites)
                     Detection frequency
                     (% samples > MRL*)
   Concentration percentiles
(all samples; fig/kg dry weight)

sediments
whole fish
bivalves

13.7 %
28.6 %
6.4 %
median
nd**
nd
nd
95th
2.7
31.9
6.4
maximum
18
260
20
after Novell, 1999
* MRL for dieldrin in sediments: 1 jig/kg; dieldrin in whole fish and bivalves: 5 jig/kg.
* *not detected in concentrations greater than MRL
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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


   Aldrin and dieldrin have been monitored under the SDWA Unregulated Contaminant
Monitoring (UCM) program since 1993 (USEPA, 1992; 57 FR 31776).  Monitoring ceased for
small public water systems (PWSs) under a direct final rule published January 8, 1999 (USEPA,
1999a; 64 FR 1494), and ended for large PWSs with promulgation of the new Unregulated
Contaminant Monitoring Regulation (UCMR) issued September 17, 1999 (USEPA, 1999b; 64
FR 50556) and effective January 1, 2001. At the time the UCMR lists were developed, the
Agency concluded there were adequate monitoring data for a regulatory determination. This
obviated the need for continued monitoring under the new UCMR list.

   3.3.1 Analytical Approach

   Currently, there is no complete national record of unregulated or regulated contaminants in
drinking water from PWSs collected under SDWA.  Many States have submitted unregulated
contaminant PWS monitoring data to EPA databases, but there are issues of data quality,
completeness, and representativeness. Nonetheless, a significant amount of State data are
available for UCM contaminants that can provide estimates of national occurrence. The
contaminant occurrence analyses findings presented in this report are based on a national cross-
section of aggregated State data (i.e., a representative subset of available State data) derived
from the Federal Safe Drinking Water Information System (SDWIS/FED) database.

   The National Contaminant Occurrence Database (NCOD) is an  interface to the actual
occurrence data stored in the Safe Drinking Water Information System (Federal version;
SDWIS/FED) and can be queried to provide a summary of the data  in SDWIS/FED for a
particular contaminant.  The drinking water occurrence data for aldrin and dieldrin presented
here were derived from monitoring data available in the SDWIS/FED database. Note, however,
that the SDWIS/FED data used in this report have undergone significant review, edit, and
filtering to meet various data quality objectives for the purposes of this analysis. Hence,  not all
data from a particular source were used; only data meeting the quality objectives described
below were included. The sources of these data, their quality  and national aggregation, and the
analytical methods used to estimate a given contaminant's national  occurrence (from these data)
are discussed in this section (for further details see USEPA, 200la,  200Ib).

   3.3.1.1  UCM Rounds 1 and 2

   The 1987 UCM contaminants include 34 volatile organic compounds (VOCs) (USEPA,
1987; 52 FR 25690).  Aldrin and dieldrin, synthetic organic compounds (SOCs), were not among
these  contaminants.  The UCM (1987) contaminants were first monitored coincident with the
Phase I regulated contaminants, during the 1988-1992 period. This period is often referred to as
"Round 1" monitoring.  The monitoring data collected by the PWSs were reported to the States
(as primacy agents), but there was no protocol in place to report these data to EPA. These data
from Round 1 were collected by EPA from many States over time and put into a database called
the Unregulated Contaminant Information  System, or URCIS.

   The 1993 UCM contaminants include 13 SOCs and 1 inorganic contaminant (IOC) (USEPA,
1992; 57 FR 31776).  Monitoring for the UCM (1993) contaminants began coincident with the
Phase II/V regulated contaminants in 1993 through 1998. This is often referred to as "Round 2"
monitoring.  The UCM (1987) contaminants were also included in the Round 2  monitoring.  As
with other monitoring data, PWSs reported these results to the States. EPA, during the past
several years, requested that the States submit these historic data to EPA and they are now stored
in the SDWIS/FED database.

   Monitoring and data collection for aldrin and dieldrin, UCM (1993) contaminants, began in
Round 2. Therefore, the following discussion regarding data quality screening, data
management, and analytical methods focuses on SDWIS/FED. Discussion of the URCIS

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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


database is included where relevant, but it is worth noting that the various quality screening, data
management, and analytical processes were nearly identical for the two databases. For further
details on the two monitoring periods as well as the databases, see USEPA (200la) and USEPA
(2001b).

    3.3.1.2  Developing a Nationally Representative Perspective

    The Round 2 data contain contaminant occurrence data from a total of 35 primacy entities
(including 34 States and data for some tribal systems).  However, data from some States are
incomplete and biased. Furthermore, the national representativeness of the data is problematic
because the data were not collected in a systematic or random statistical framework.  These State
data could be heavily skewed to low-occurrence or high-occurrence settings. Hence, the State
data were evaluated based on pollution-potential indicators and the spatial/hydrologic diversity
of the nation.  This evaluation enabled the construction of a cross-section from the available
State data sets that provides a reasonable representation of national occurrence.

    A national cross-section comprised of the Round 2  State contaminant occurrence databases
was established using the approach developed for the EPA report^ Review of Contaminant
Occurrence in Public Water Systems (USEPA, 1999d). This approach was developed to support
occurrence analyses for EPA's Chemical Monitoring Reform (CMR) evaluation, and was
supported by peer reviewers and stakeholders. The approach cannot provide a "statistically
representative" sample because the original monitoring data were not collected or reported in an
appropriate fashion.  However, the resultant "national cross-section" of States should provide a
clear indication of the central tendency of the national data. The remainder of this section
provides a summary description of how the national cross-section from the SDWIS/FED (Round
2) database was developed. The details of the approach are presented  in other documents
(USEPA, 200la, 2003b); readers are referred to these for more specific information.

    3.3.1.2.1  Cross-Section Development

    As a first step in developing the cross-section, the State data contained in the SDWIS/FED
database (that contains the Round 2 monitoring results) were evaluated for completeness and
quality. Some States reported only detections, or their data had incorrect units. Data sets only
including detections are obviously biased, over-representing high-occurrence settings.  Other
problems included substantially incomplete data sets without  all PWSs reporting (USEPA,
200la; Sections II and III).

    The balance of the States remaining after the data quality  screening were then examined to
establish a national cross-section.  This  step was based on evaluating the States' pollution
potential and geographic coverage in relation to all States. Pollution potential is considered to
ensure a selection of States that represent the range of likely contaminant occurrence and a
balance with regard to likely high and low occurrence.  Geographic  consideration is included so
that the wide range of climatic and hydrogeologic conditions across the United States are
represented, again balancing the varied  conditions that  affect transport and fate of contaminants,
as well as conditions that affect naturally occurring contaminants (USEPA, 200Ib; Sections
III.A. and III.B.).

    The cross-section States were  selected to represent a variety of pollution potential conditions.
Two primary pollution potential indicators were used.  The first factor selected indicates
pollution potential from manufacturing/population density and serves as an indicator of the
potential for VOC contamination within a State.  Agriculture was selected as the second
pollution potential indicator because the majority of SOCs of concern  are pesticides (USEPA,
200Ib; Section III.A.).  The 50 individual States were ranked from highest to lowest based on
the  pollution potential indicator data. For example, the State with the highest ranking for

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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


pollution potential from manufacturing received a ranking of 1 for this factor and the State with
the lowest value was ranked as number 50.  States were ranked for their agricultural chemical
use status in a similar fashion.

    The States' pollution potential rankings for each factor were subdivided into four quartiles
(from highest to lowest pollution potential).  The cross-section States were chosen equally for
both pollution potential factors to ensure representation, for example, from: States with high
agrochemical pollution potential rankings and high manufacturing pollution potential rankings;
States with high agrochemical pollution potential rankings and low manufacturing pollution
potential rankings; States with low agrochemical pollution potential rankings and high
manufacturing pollution potential rankings; and States with low agrochemical pollution potential
rankings and low manufacturing pollution potential rankings (USEPA, 2001b; Section III.B.).  In
addition, some secondary pollution potential indicators were considered to further ensure that the
cross-section States included the spectrum of pollution potential conditions (high to low).  At the
same time, States within the specific quartiles were considered collectively across all quartiles to
attempt to provide a geographic coverage across all regions of the United States.

    The data quality screening, pollution potential rankings, and geographic coverage analysis
established a national cross-section of 20 Round 2 (SDWIS/FED) States.  The cross-section
States provide good representation of the nation's varied climatic and hydrogeologic regimes and
the breadth of pollution potential for the contaminant groups (Figure 3-1).

    3.3.1.2.2  Cross-Section Evaluation

    To evaluate and validate the method for creating the national cross-sections, the method was
used to create smaller State subsets from the 24-State, Round  1 (URCIS) cross-section. Again,
States were chosen to achieve a balance from the quartiles describing pollution potential, and a
balanced geographic distribution, to incrementally build subset cross-sections of various sizes.
For example, the Round 1 cross-section was tested with subsets of 4, 8 (the first 4 State subset
plus 4 more States), and 13 (8 State subset plus 5) States.  Two additional cross-sections were
included in the analysis for comparison: a cross-section composed of 16 States with biased data
sets eliminated from the 24 State cross-section for data quality reasons, and a cross-section
composed of all 40 Round 1 States (USEPA, 2001b; Section III.B. 1).

    These Round 1 incremental cross-sections were then used to evaluate occurrence for an array
of both high and low occurrence contaminants.  The comparative results illustrate several points.
The results are quite stable and consistent for the 8-, 13- and 24-State cross-sections. They are
much less so  for the 4-State, 16-State (biased), and 40 State (all Round 1 States) cross-sections.
The 4-State cross-section is apparently too small to provide balance both geographically and
with pollution potential, a finding that concurs with past work (USEPA, 1999d).  The CMR
analysis suggested that a minimum of 6-7 States was needed to provide balance both
geographically and with pollution potential,  and the CMR report used 8 States out of the
available data for its nationally representative cross-section  (USEPA, 1999d). The 16-State and
40-State cross-sections, both including biased States, provided occurrence results that were
unstable and inconsistent for a variety of reasons associated with their data quality problems
(USEPA, 2001b; Section III.B. 1).
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Figure 3-1: Geographic distribution of cross-section States for Round 2 (SDWIS/FED)
   Round 2 (SDWIS/FED) Cross Section
   States
   Alaska
   Arkansas
   Colorado
   Kentucky
   Maine
   Maryland
   Massachusetts
   Michigan
   Minnesota
   Missouri
New Hampshire
New Mexico
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Rhode Island
Texas
Washington
    The 8-, 13-, and 24-State cross-sections provide very comparable results, are consistent, and
are usable as national cross-sections to provide estimates of contaminant occurrence.  Including
greater data from more States improves the national representation and the confidence in the
results, as long as the States are balanced related to pollution potential and spatial coverage. The
20-State cross-section provides the best, nationally representative cross-section for the Round 2
data.

    3.3.1.3 Data Management and Analysis

    The cross-section analyses focused on occurrence at the water system level;  i.e., the
summary data presented discuss the percentage of public water systems with detections, not the
percentage of samples with detections. By normalizing the analytical data to the system level,
skewness inherent in the sample data is avoided.  System level analysis was used since a PWS
with a known contaminant problem usually has to sample more frequently than a PWS that has
never detected the contaminant. Obviously, the results of a simple computation of the
percentage of samples with detections (or other statistics) can be skewed by the  more frequent
sampling results reported by the contaminated site. This level of analysis is conservative. For
example, a system need only have a single sample with an analytical result greater than  the
MRL, i.e., a detection, to be counted as a system with a result "greater than the MRL."

    Also, the data used in the analyses were limited to only those data with confirmed water
source and sampling type information.  Only standard SDWA compliance samples were used;
"special" samples, or "investigation" samples (investigating a contaminant problem that would
bias results), or samples of unknown type were not used in the analyses. Various quality control
and review checks were made of the results, including follow-up questions to the States
providing the data.  Many of the most intractable data quality problems encountered occurred
with older data.  These problematic data were, in some cases, simply eliminated from the
analysis. For example, when the number of problematic data were insignificant relative to the
total number of observations, they were dropped from the analysis (For further details see
Cadmus, 2000).

    As indicated above, Massachusetts is included in the 20-State, Round 2 national cross-
section.  Although noteworthy for the presence of SOCs like aldrin and dieldrin, Massachusetts
SOC data were problematic.  Massachusetts reported Round 2 sample results for SOCs from
only 56 PWSs, while reporting VOC results from over 400 different PWSs. Massachusetts SOC
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data also contained an atypically high percentage of systems with analytical detections when
compared to all other States. Through communications with Massachusetts data management
staff it was learned that the State's SOC data were incomplete and that the SDWIS/FED record
for Massachusetts SOC data was also incomplete. For instance, the SDWIS/FED Round 2 data
for Massachusetts indicate 18% of systems reported detections of aldrin and dieldrin. The States
with the next highest detection frequencies reported only 0.2% and 0.4% of systems with
detections for aldrin and dieldrin, respectively.  In contrast, Massachusetts data characteristics
and quantities for lOCs and VOCs were reasonable and comparable with other States' results.
Therefore, Massachusetts was included in the group of 20 SDWIS/FED Round 2 cross-section
States with usable data for lOCs and VOCs, but its aldrin and dieldrin (SOC) data were omitted
from Round 2 cross-section occurrence analyses and summaries presented in this report.

   3.3.1.4 Occurrence Analysis

   To evaluate national contaminant occurrence, a two-stage analytical approach has been
developed. The first stage of analysis provides  a straightforward, conservative, non-parametric
evaluation of occurrence of the CCL regulatory determination priority contaminants as described
above. These Stage 1 descriptive statistics are summarized here.  Based in part on the findings
of the Stage 1 Analysis, EPA will determine whether more rigorous parametric statistical
evaluations, the Stage 2 Analysis, may be warranted to generate national probability estimates of
contaminant occurrence and exposure for priority contaminants (for details on this two stage
analytical approach see Cadmus, 2000; USEPA, 2002b).

   The summary descriptive statistics presented in Table 3-4 for aldrin and in Table 3-5 for
dieldrin are a result of the Stage 1 analysis and include data from Round 2 (SDWIS/FED, 1993-
1997) cross-section States (excluding Massachusetts).  Included are the total number of samples,
the percent samples with detections, the 99th percentile concentration of all samples, the 99th
percentile concentration of samples with detections, and the median concentration of samples
with detections.  The percentages of PWSs and  population  served indicate the proportion of
PWSs whose analytical results showed a detect!on(s) of the contaminant (simple detection, >
MRL) at any time during the monitoring period; or a detect!on(s) greater than half the Health
Reference Level (HRL); or a detecton(s) greater than the Health Reference Level. The Health
Reference Level for aldrin and dieldrin, 0.002 |ig/L, is a preliminary estimated health effect level
used for this analysis (EPA derived the HRL based on cancer potency selecting the most
conservative, and therefore the most protective, value corresponding to the one-in-a-million (1 x
10"6) cancer risk level).

   The 99th percentile concentration is used here as a summary statistic to indicate the upper
bound of occurrence values because maximum values can be extreme values (outliers) that
sometimes result from sampling or reporting error. The 99th percentile concentration is presented
for only the samples with detections and for all  of the samples because the value for the 99th
percentile concentration of all samples is below the Minimum Reporting Level (MRL) (denoted
by "<" in Tables 3-4 and 3-5).  For the same reason, summary statistics such as the 95th
percentile concentration of all samples or the  median (or mean) concentration of all samples are
omitted because these also are all "<" values.  This is the case because only 0.006% (aldrin) and
0.064% (dieldrin) of all samples recorded detections in Round 2.

   As a simplifying assumption, a value of half the MRL is often used as an estimate of the
concentration of a contaminant in samples/systems whose results are less than the MRL. For
contaminants with relatively low occurrence such as aldrin and dieldrin in drinking water
occurrence databases, the median or mean value of occurrence using this assumption would be
half the MRL (0.5 * MRL).  However, for these occurrence data this is not straightforward. For
Round 2, States have reported a wide range of values for the MRLs.  This is in part related to
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State data management differences as well as real differences in analytical methods, laboratories,
and other factors.

   The situation can cause confusion when examining descriptive statistics for occurrence. For
example, most Round 2 States reported non-detections simply as zeroes resulting in a modal
MRL value of zero. By definition the MRL cannot be zero. This is an artifact of State data
 management systems. Because a simple meaningful summary statistic is not available to
describe the various reported MRLs, and to avoid confusion, MRLs are not reported in the
summary tables (Tables 3-4 and 3-5).

   In Tables 3-4 and 3-5, national occurrence is estimated by extrapolating the summary
statistics for the 20-State cross-section (excluding Massachusetts) to national numbers for
systems, and population served by  systems, from the Water Industry Baseline Handbook, Second
Edition (USEPA, 2000d). From the handbook, the total number of community water systems
(CWSs) plus non-transient, non-community water systems (NTNCWSs) is 65,030, and the total
population served by CWSs plus NTNCWSs is 213,008,182 persons (see Tables 3-4 and 3-5).
To generate the estimate of national occurrence based on the cross-section occurrence findings,
the national number of PWSs (or population  served by PWSs) is simply multiplied by the
percentage value for the particular  cross section occurrence statistic (e.g. the national estimate
for the total number of PWSs with  detections (11) is the product of the total national number of
PWSs (65,030) and the percentage of PWSs with detections (0.016%)).

   Included in Tables 3-4 and 3-5, in addition to the cross-section data results,  are results and
national extrapolations from all Round 2 reporting States.  The data from the biased States are
included because of the very low occurrence of aldrin and dieldrin in drinking water samples in
all States. For contaminants with very low occurrence, such as aldrin and dieldrin where very
few States have detections, any occurrence becomes more important, relatively.  For such
contaminants, the cross-section process can easily miss a State with occurrence that becomes
more important.  This is the case with aldrin  and dieldrin.

   Extrapolating only from the cross-section States, the very low occurrence of aldrin and
dieldrin clearly underestimates national occurrence.  For example, while data from biased States
like Alabama (reporting 100% detections >HRL, >V2 HRL, and >MRL for both aldrin and
dieldrin) exaggerate occurrence because only systems with detections reported results, their
detections are real and need to be accounted for because extrapolations from the cross-section
States do not predict enough detections in the biased States. Therefore, results from all reporting
Round 2 States, including the biased States, are also used here to extrapolate to a national
estimate. Using the biased States'  data should provide conservative  estimates, likely
overestimates, of national occurrence for aldrin and dieldrin.

   As exemplified by the cross-section extrapolations for aldrin and dieldrin, national
extrapolations of these Stage 1 analytical results can be problematic, especially for contaminants
with very low occurrence, because the State data used for the cross-section are not a strict
statistical sample. For this reason,  the nationally extrapolated estimates of occurrence based on
Stage 1 results are not presented in the Federal Register Notice. The presentation in the Federal
Register Notice of only the actual results of the cross-section analysis maintains a straight-
forward presentation, and the integrity of the data, for stakeholder review. The nationally
extrapolated Stage 1 occurrence values are presented here, however, to provide additional
perspective. A more rigorous statistical modeling effort, the Stage 2 analysis, could be
conducted on the cross-section data (USEPA, 2002b). The Stage 2 results would be more
statistically robust and more suitable to national extrapolation.  This  approach would provide a
probability estimate and would also allow for better quantification of estimation error.
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    3.3.1.5 Additional Drinking Water Data from the Corn Belt

    To augment the SDWA drinking water data analysis described above, and to provide
additional coverage of the corn belt States where the use of aldrin and dieldrin as agricultural
insecticides was historically high, independent analyses of SDWA drinking water data from the
States of Iowa, Illinois, and Indiana are reviewed below.  Raw water aldrin and dieldrin
monitoring data are also included from rural, private water supply wells in Illinois.

    The Iowa analysis examined SDWA compliance monitoring data from surface and ground
water PWSs for the years 1988-1995 (Hallberg et al., 1996). Illinois and Indiana compliance
monitoring data for surface and ground water PWSs were evaluated mostly for the years after
1993, though some earlier data were also included (USEPA, 1999d). The raw water data from
Illinois were collected from rural, private supply wells (Goetsch et al., 1992).  Data sources, data
quality, and analytical methods for these analyses are described in the respective reports; they
were all treated similarly to the data quality reviews for this analysis.
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   3.3.2 Results

   3.3.2.1  Aldrin

   3.3.2.1.1  Occurrence Estimates

   The percentages of PWSs with detections of aldrin are very low (Table 3-4).  The cross-
section shows only approximately 0.02% of PWSs (approximately 11 PWSs nationally)
experienced detections at any concentration level (>MRL, >1A> HRL, and >HRL), affecting about
0.02% of the population served (approximately 40,000-50,000 people nationally) (see also
Figure 3-3). All of the detections were in systems using ground water.  The percentage of PWSs
(or population served) in a given source category (i.e., ground water) with detections >MRL, >!/2
HRL, or >HRL is the same because the estimated HRL is lower than the MRL. Hence, any
detection reported is also greater than the HRL. While concentrations are low  for the
detections the median concentration is 0.58 |ig/L and the 99th percentile concentration is 0.69
|ig/L  these values are greater than the HRL.

   As noted above, because of the very low occurrence, the cross-section States yield an
underestimate.  Hence, all data are used, even the biased data, to present a conservative upper
bound estimate.  Conservative estimates of aldrin occurrence using all of the Round 2 reporting
States still show relatively low detection frequencies (Table 3-4). Approximately 0.2% of PWSs
(estimated at 138 PWSs  nationally) experienced detections at any concentration level (>MRL,
>l/2 HRL, and >HRL), affecting about 0.5% of the population served (approximately 1,052,000
people nationally). The  proportion of surface water PWSs with detections was greater than
ground water systems. Again the percentages of PWSs (or populations served) with detections
>MRL, >l/2 HRL, or >HRL are the same because of the low HRL.  The median concentration of
detections is 0.18 |ig/L and the 99th percentile concentration is 4.4 |ig/L.

   The Round 2 reporting States and the Round 2 national cross-section  show a proportionate
balance in PWS source waters compared to the national inventory. Nationally, 91% of PWSs
use ground water (and 9% surface waters): Round 2 reporting States and the Round 2 national
cross-section show that 87% use ground water (and  13% surface waters). The relative
populations served are not as comparable. Nationally, about 40% of the population is served by
PWSs using ground water (and 60% by surface water). For the Round 2 cross-section, 29% of
the cross-section population is served by ground water PWSs (and 71% by surface water). For
all Round 2 reporting States, 31% of the population  is served by ground water PWSs (and 69%
by surface water). As a consequence of these disproportions, the resultant national
extrapolations are not additive.

   Drinking water data from the corn belt States of Iowa, Indiana, and Illinois also show very
low occurrence of aldrin. There were no detections  of the pesticide in the Iowa or Indiana
SDWA compliance monitoring data for  surface or ground water PWSs  (Hallberg et al., 1996;
USEPA, 1999d).  While Illinois also had no detections of the compound in ground water PWSs,
it was detected in surface water PWSs in that State.  Occurrence was low with 1.8% of surface
water systems, and 0.10% of samples, showing detections. The 99th percentile concentration of
all samples was below the reporting level and the maximum concentration was 2.4 jig/L
(USEPA, 1999d). A survey of Illinois rural, private water supply wells showed very low
occurrence of aldrin as well.  Only 0.3% of all sampled wells had detections at a reporting limit
of 0.004 |ig/L (Goetsch et al., 1992).
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Table 3-4:  Summary occurrence  statistics  for aldrin


Frequency Factors
Total Number of Samples
Percent of Samples with Detections
99 Percentile Concentration (all samples)
Health Reference Level
Minimum Reporting Level (MRL)
99 Percentile Concentration of Detections
Median Concentration of Detections
Total Number of PWSs
Number of GW PWSs
Number of SW PWSs
Total Population
Population of GW PWSs
Population of SW PWSs
Occurrence by System
% PWSs with detections (> MRL)
Range of Cross-Section States
GW PWSs with detections
SW PWSs with detections
% PWSs > 1/2 Health Reference Level (HRL)
Range of Cross-Section States
GW PWSs > 1/2 Health Reference Level
SW PWSs > 1/2 Health Reference Level
% PWSs > Health Reference Level
Range of Cross-Section States
GW PWSs > Health Reference Level
SW PWSs > Health Reference Level
Occurrence by Population Served
% PWS Population Served with detections
Range of Cross-Section States
GW PWS Population with detections
SW PWS Population with detections
% PWS Population Served > 1/2 Health Reference Level
Range of Cross-Section States
GW PWS Population > 1/2 Health Reference Level
SW PWS Population > 1/2 Health Reference Level
% PWS Population Served > Health Reference Level
Range of Cross-Section States
GW PWS Population > Health Reference Level
SW PWS Peculation > Health Reference Level
20 State
Cross -Sect ion
(Round 2)
31,083
0.006%
< (Non-detect)
0.002 ug/L
Variable
0.69 ug/L
0.58 ug/L
12,165
10,540
1,625
47,708,156
14,043,051
33,665,105

0.016%
0 - 0.23%
0.019%
0.000%
0.016%
0 - 0.23%
0.019%
0.000%
0.016%
0 - 0.23%
0.019%
0.000%

0.018%
0 - 0.35%
0.062%
0.000%
0.018%
0 - 0.35%
0.062%
0.000%
0.018%
0 - 0.35%
0.062%
0.000%
All Reporting
States
(Round 2)
41,565
0.132%
< (Non-detect)
0.002 ug/L
Variable
4.40 ug/L
0.18 ug/L
15,123
13,195
1,928
58,979,361
18,279,343
40,700,018

0.212%
0 - 100 %
0.167%
0.519%
0.212%
0 - 100 %
0.167%
0.519%
0.212%
0 - 100 %
0.167%
0.519%

0.494%
0 - 100 %
0.414%
0.530%
0.494%
0 - 100 %
0.414%
0.530%
0.494%
0 - 100 %
0.414%
0.530%
National System &
3
Population Numbers
-
-
-
-
-
-
-
65,030
59,440
5,590
213,008,182
85,681,696
127,326,486
National Extrapolation
11
N/A
11
0
11
N/A
11
0
11
N/A
11
0
138
N/A
99
29
138
N/A
99
29
138
N/A
99
29

39,000
N/A
53,000
0
39,000
N/A
53,000
0
39,000
N/A
53,000
0
1,052,000
N/A
355,000
674,000
1,052,000
N/A
355,000
674,000
1,052,000
N/A
355,000
674.000
1.  Summary Results based on data from 20-State Cross-Section (minus Massachusetts), from SDWIS/FED, UCM (1993) Round 2.
2.  Summary Results based on data from all reporting, States from SDWIS/FED, UCM (1993) Round 2.
3.  Total PWS and population numbers are from EPA March 2000 Water Industry Baseline Handbook.
4.  See Section 3.3.1.4 for discussion.
5.  National extrapolations are from the 20-State cross-section data (left) and all Round 2 States reporting data (right) using the Baseline Handbook system and population numbers.
- PWS = Public Water Systems'  GW = Ground Water'  SW = Surface Water; MRL = Minimum Reporting Level (for laboratory analyses);
HRL = Health Reference Level  an estimated health effect level usedfor preliminary assessment for this review; N/A = Not Applicable. "
- The Health Reference Level (HRL) used for aldrin is 0.002 jJg/L. This is a draft value for working review only.
- Total Number of Samples = the total number of analytical records for aldrin.
- 99th Percentile Concentration = the concentration value of the 99th per'centile of either all analytical results or just the detections (in jjg/L)
- Median Concentration of Detections = the median analytical value of all the detections (analytical results greater than the MRL) (in [ig/L).
- Total Number of PWSs = the total number of public water systems with records for aldrin
- Total Population Served = the total population served by public water systems with records for aldrin
- % PWS with detections,  % PWS > y? Health Reference Level, % PWS > Health Reference Level = percent of the total number of public water systems with at least one analytical result that
exceeded the MRL, !A Health Reference Level  Health Reference Level, respectively
- % PWS Population Served with detections, % PWS Population Served >% Health Reference Level, % PWS Population Served > Health Reference Level = percent of the total population served
by PWSs with at least one analytical result exceeding the MRL, !A Health Reference Level, or the Health Reference Level, respectively
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Figure 3-2:  States with PWSs with detections of aldrin for all States with data in
SDWIS/FED (Round 2)
                                                  All States
                                                              Aldrin Detects in All Round 2 States
                                                                 | States not in Round 2
                                                               ^| No data for Aldrin
                                                               3 States with No Detections (No PWSs > MRL)
                                                                States with Detections (Any PWSs > MRL)
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Figure 3-3:  Round 2 cross-section States with PWSs with detections of aldrin (any PWSs
with results greater than the Minimum Reporting Level [MRL]; above) and concentrations
greater than the Health Reference Level (HRL; below)
                                        O
Aldrin Occurrence in Cross-section States
    States not in Cross-Section
    No data for Aldrin
    000% PWSs > MRL
    0.01 - 1.00% PWSs > MRL
    > 1.00% PWSs> MRL*
                                                           Aldrin Occurrence in Cross-section States
                                                           |    | States not in Cross-Section
                                                           |    | No data for Aldrin
                                                           |    j 0 00% PWSs > HRL
                                                                0.01 - 1.00% PWSs > HRL
                                                                1.00% PWSs > HRL
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3.3.2.1.2 Regional Patterns

    Occurrence results are displayed graphically by State in Figures 3-2 and 3-3 to assess
whether any distinct regional patterns of occurrence are present.  Thirty-four States reported
Round 2 data but seven of those States have no data for aldrin (Figure 3-2). Another 22 States
did not detect aldrin.  The remaining 5 States have detected aldrin in drinking water and are
generally located either in the southern United States or the Northeast (Figure 3-2). In contrast
to the summary statistical data presented in the previous section, this simple spatial analysis
includes the biased Massachusetts data.

    The simple spatial analysis presented in Figures 3-2 and 3-3 suggests that special regional
analyses are not warranted. The State of Alabama does, however, stand out as having relatively
high occurrence for reasons that are unclear.  While there is a weak geographic clustering of
drinking water detections in a few southern and northeastern States (including the State of
Massachusetts' biased data), this is partly the result of so few States with any detections.
Further, use and environmental release information described in section 3.1 of this report
indicates that aldrin detections are more widespread than the drinking water data suggest. Two
out of the three TRI States (Arkansas and Michigan) that reported releases of aldrin into the
environment did not report detections of the chemical in PWS sampling. Furthermore, aldrin's
widespread presence in the environment is evidenced by detections of the compound in
hazardous waste sites in at least 31 States (at NPL sites), as well  as detections in site samples in
at least 40 States (listed in ATSDR's HazDat).

    3.3.2.2 Dieldrin

    3.3.2.2.1  Occurrence Estimates

    The percentages of PWSs with detections are very low (Table 3-5). The cross-section shows
approximately 0.1% of PWSs (about 61 PWSs nationally) experienced detections at any
concentration level (>MRL, >l/2 HRL, and >FIRL), affecting less than 0.1% of the population
served (approximately 150,000 people nationally) (see also Figure 3-5).  The percentages of
PWSs (or population served) in a given source category (i.e.,  ground water) with detections
greater than the MRL, l/2 HRL, or HRL are the same because  the estimated HRL is  less than the
MRL.  Hence, any detection reported is also greater than the HRL. Detection frequencies are
marginally higher for surface water systems when compared to ground water systems.  While
concentrations are also low  for samples with detections the median concentration is 0.16 |ig/L
and the 99th percentile concentration is 1.36 jig/L  these values are greater than the HRL.

    As noted above, because of the very low occurrence, the cross-section  States yield  an
underestimate.  Hence, all data are used, even the biased data, to present a  conservative upper
bound estimate.  Conservative estimates of dieldrin occurrence using all of the Round 2
reporting States still show relatively low detection frequencies (Table 3-5). Approximately 0.2%
of PWSs (estimated at 137 PWSs nationally) experienced detections at any concentration level
(>MRL, >!/2 HRL, and >HRL), affecting about 0.4% of the population served (approximately
793,000 people nationally).  The proportion of surface water PWSs with detections was greater
than ground water systems. Again the percentages of PWSs (or populations served) with
detections greater than the MRL, l/2 HRL, or HRL are the same because of the low HRL. The
median concentration of detections is 0.42 |ig/L and the 99th percentile concentration is 4.4 |ig/L.

    The Round 2 reporting States and the Round 2 national cross-section show a proportionate
balance in PWS source waters compared to the national inventory. Nationally, 91% of PWSs
use
ground water (and 9% surface waters): Round 2 reporting States and the Round 2 national cross-
section show that 88% use ground water (and  12% surface waters).  The relative populations

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served are not similarly comparable. Nationally, about 40% of the population is served by PWSs
using ground water (and 60% by surface water). For the Round 2 cross-section, 30% of the
cross-section population is served by ground water PWSs (and 70% by surface water).  For all
Round 2 reporting States, 32% of the population is served by ground water PWSs (and 68% by
surface water). As a consequence of these disproportions, the resultant national  extrapolations
are not additive.

   Drinking water data from the corn belt States of Iowa, Indiana, and Illinois also show very
low occurrence of dieldrin.  There were no detections of the pesticide in the Iowa SDWA
compliance monitoring data for surface or ground water PWSs (Hallberg et al, 1996). While
Illinois and Indiana also had no detections of the compound in ground water PWSs, it was
detected in surface water PWSs in those States (USEPA, 1999d).  Occurrence was low in both
States: 1.8% of surface water systems (0.1% of samples) showed detections in Illinois and 2.1%
of surface water systems (0.3% of samples)  showed detections in Indiana. For Illinois and
Indiana surface water PWSs, the 99th percentile concentrations of all samples were below the
reporting level and the maximum concentrations were 0.1 |ig/L and 0.04 |ig/L, respectively
(USEPA, 1999d). Furthermore, in a survey  of rural, private water supply wells in Illinois, only
1.6% of all sampled wells had detections of dieldrin (Goetsch et al., 1992).

   3.3.2.2.2  Regional Patterns

   Occurrence results are displayed graphically by State in Figures 3-4 and 3-5  to assess
whether any distinct regional patterns of occurrence are present.  Thirty-four States reported
Round 2 data but 7 of those States have no data for dieldrin (Figure 3-4). Another 19 States did
not detect dieldrin. The remaining 8 States detected dieldrin in drinking water, and are generally
located either in the southern United States or  in the Northeast (Figure 3-4). In contrast to the
summary statistical data presented in the previous section, this simple  spatial analysis includes
the biased Massachusetts data.

   The simple spatial analysis presented in  Figures 3-4 and 3-5 suggests that special regional
analyses are not warranted.  The State of Alabama does, however, stand out as having relatively
high occurrence for reasons that are unclear. While there is a weak geographic clustering of
drinking water detections in a few southern  and northeastern States (including the State of
Massachusetts' biased data), this is partly  the result of so few States with any detections.
Further, use  and environmental release information (section 3.1) and ambient water quality data
(section 3.2) indicate that dieldrin detections are more widespread than the drinking water data
suggest. Detections of the compound in hazardous waste sites in at least 38 States (at NPL
sites), site samples in at least 40 States (listed in ATSDR's HazDat), and water, sediment, and
biotic tissue  quality data from the NAWQA program provide evidence for nationwide
occurrence.

3.4 Conclusion

   Aldrin has been detected at very  low frequencies and concentrations in bed sediments
sampled during the first round of the USGS  NAWQA studies.  Aldrin  releases have been
reported through TRI. Dieldrin has been detected at low frequencies and concentrations in
ground and surface water sampled during  the first round of the USGS NAWQA studies, and at
similar frequencies and concentrations in  surface waters of the Mississippi River and major
tributaries. Dieldrin occurrence is greater in stream bed sediments and biotic tissue, however.
Both  aldrin and dieldrin have been found  at  ATSDR HazDat and CERCLA NPL sites across the
country.

   Aldrin and dieldrin have been detected in PWS samples collected under SDWA. Occurrence
estimates are very low with only 0.006% and 0.06% of all cross-section samples showing

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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


detections for aldrin and dieldrin, respectively. Significantly, the values for the 99th percentile
and median concentrations of all cross-section samples are less than the MRL for both
contaminants. For Round 2 cross-section samples with detections, the median concentration for
aldrin is 0.58 |ig/L and the 99th percentile  concentration is 0.69 |ig/L. Dieldrin Round 2 cross-
section samples with detections show median and 99th percentile concentrations of 0.16 |ig/L and
1.36 |ig/L,  respectively.  Systems with detections constitute only 0.02% of Round 2 cross-section
systems (an estimate of 11 systems, nationally) for aldrin, and 0.1% of Round 2 cross-section
systems (about 61 systems, nationally) for dieldrin.

   National estimates for the population served by PWSs with detections are also very low
(40,000-50,000 for aldrin and 150,000 for dieldrin), and are the same for all categories (>MRL,
>l/2 HRL, >HRL).  These estimates constitute less than 0.02% of the national population for
aldrin and less than 0.1% of the national population for dieldrin. Using more conservative
estimates of occurrence from all States reporting SDWA Round 2  monitoring data, including
States with biased data, 0.2%  of the nation's PWSs (approximately 138 systems) and 0.5% of the
PWS population served (approximately 1,052,000 people) are estimated to have aldrin detections
greater than the MRL, 1A HRL, and HRL.  More conservative estimates for dieldrin show that
0.2% of the nation's PWSs (approximately 137 systems) and 0.4% of the PWS population served
(approximately 793,000 people) are estimated to have detections of dieldrin greater than the
MRL, half the HRL,  and the HRL.

Additional  SDWA compliance data from the corn belt States of Iowa, Indiana, and Illinois
examined through independent analyses support the drinking water data analyzed in this report.
There were no detections of aldrin or dieldrin in either surface or ground water PWSs in Iowa.
Illinois reported aldrin and dieldrin detections from surface water PWSs only, with 1.8% of
surface water systems (0.1% of samples) showing aldrin occurrence and 1.8% of surface water
systems (0.1% of samples) showing dieldrin occurrence.  Indiana reported no detections of aldrin
in either surface or ground water, though 2.1% of surface water systems (0.3% of samples)
reported dieldrin detections.  The 99th percentile concentration of all aldrin samples was below
the reporting level and the maximum concentration was 2.4 |ig/L.  The 99th percentile
concentrations of all  dieldrin samples from Illinois and Indiana were also below the reporting
level while the maximum concentrations were 0.1 |ig/L and 0.04 |ig/L, respectively (USEPA,
1999d). Further, in a survey of rural, private water supply wells in Illinois, aldrin and dieldrin
were detected in only 0.3% and 1.6% of all sampled wells, respectively.


4.0 HEALTH EFFECTS

   A full description of the health effects and the dose-response information for threshold and
non-threshold effects associated with exposures to aldrin or dieldrin are presented in Chapters 7
and 8 of the Drinking Water Support Document for Aldrin and Dieldrin (USEPA, 2003b). A
summary of the pertinent findings are presented below.

4.1 Hazard Characterization and Mode of Action Implications

   Following acute exposure to high doses, the primary adverse health effects of aldrin and
dieldrin in humans are those resulting from neurotoxicity to the central nervous system,
including hyperirritability, convulsions and coma (Jager, 1970; Spiotta, 1951; ACGIH, 1984).  In
some cases, these may be followed by cardiovascular effects such as unusually rapid beating of
the heart and elevated blood
                                           26

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Regulatory Determination Support Document for Aldrin and Dieldrin
July 2003
      Table 3-5:  Summary  occurrence statistics for dieldrin


Frequency Factors
Total Number of Samples
Percent of Samples with Detections
99 Percentile Concentration (all samples)
Health Reference Level
Minimum Reporting Level (MRL)
99 Percentile Concentration of Detections
Median Concentration of Detections
Total Number of PWSs
Number of GW PWSs
Number of SW PWSs
Total Population
Population of GW PWSs
Peculation of SW PWSs
Occurrence bv System
% PWSs with detections (> MRL)
Range of Cross-Section States
GW PWSs with detections
SW PWSs with detections
% PWSs > 1/2 Health Reference Level (HRL)
Range of Cross-Section States
GW PWSs > 1/2 Health Reference Level
SW PWSs > 1/2 Health Reference Level
% PWSs > Health Reference Level
Range of Cross-Section States
GW PWSs > Health Reference Level
SW PWSs > Health Reference Level
Occurrence by Population Served
% PWS Population Served with detections
Range of Cross-Section States
GW PWS Population with detections
SW PWS Population with detections
% PWS Population Served > 1/2 Health Reference Level
Range of Cross-Section States
GW PWS Population > 1/2 Health Reference Level
SW PWS Population > 1/2 Health Reference Level
% PWS Population Served > Health Reference Level
Range of Cross-Section States
GW PWS Population > Health Reference Level
SW PWS Peculation > Health Reference Level
20 State
C ross-S6ction
(Round 2)
29,603
0.064%
< (Non-detect)
0.002 ug/L
17 -II4
Variable
1.36 ug/L
0.16 ug/L
11,788
10,329
1,459
45,784,187
13,831,864
31.952.323

0.093%
0 - 0.97%
0.087%
0.137%
0.093%
0 - 0.97%
0.087%
0.137%
0.093%
0 - 0.97%
0.087%
0.137%

0.070%
0 - 2.00%
0.146%
0.038%
0.070%
0 - 2.00%
0.146%
0.038%
0.070%
0 - 2.00%
0.146%
0.038%
All Reporting
States2
(Round 2)
40,055
0.135%
< (Non-detect)
0.002 ug/L
Variable
4.40 ug/L
0.42 ug/L
14,725
12,968
1,757
56,909,027
18,044,000
38.865.027

0.211%
0 - 100%
0.177%
0.455%
0.211%
0 - 100%
0.177%
0.455%
0.211%
0 - 100%
0.177%
0.455%

0.372%
0 - 100%
0.371%
0.372%
0.372%
0 - 100%
0.371%
0.372%
0.372%
0 - 100%
0.371%
0.372%
National System &
3
Population Numbers
-
-
-
-
-
-
-
65,030
59,440
5,590
213,008,182
85,681,696
127.326.486
National Extrapolation
61
N/A
52
8
61
N/A
52
8
61
N/A
52
8
137
N/A
105
25
137
N/A
105
25
137
N/A
105
25

150,000
N/A
125,000
48,000
150,000
N/A
125,000
48,000
150,000
N/A
125,000
48.000
793,000
N/A
318,000
474,000
793,000
N/A
318,000
474,000
793,000
N/A
318,000
474.000
1.  Summary Results based on data from 20-State Cross-Section (minus Massachusetts) from SDWIS/FED, UCM (1993) Round 2.
2.  Summary Results based on datafrom all reporting States from SDWIS/FED, UCM (1993) Round 2; see text for jurther discussion.
3.  Total PWS and population numbers are from EPA March 2000 Water Industry Baseline Handbook.
4.  See Section 3.3.1.4 for discussion
5.  National extrapolations are from the 20-State cross-section data (left) and all Round 2 States reporting data (right) using the Baseline Handbook system and population numbers.
- "P WS = Public Water Systems; GW = Ground Water; SW = Surface Water; MRL = Minimum Reporting Level nor laboratory analyses);
HRL= Health Reference Level, an estimated health effect level used for preliminary assessment for this review; NtA = Not Applicable '
- The Health Reference Level (HRL) used for dieldrin is 0.002 j-ig/L.  This is a draft value for working review only.
- Total Number of Samples = the total number of analytical records for dieldrin
- 99th Percentile Concentration = the concentration value  of the 99th per'centile of either all analytical results or just the detections (in jjg/L)
- Median Concentration of Detections = the median analytical value of all the detections (analytical results greater than the MRL) (in f-ig/L)
- Total Number of PWSs = the total number of public water systems with records for dieldrin
- Total Population Served = the total population served by public water systems with records for dieldrin
- % PWS with detections,  % PWS > y? Health Reference Level, % PWS > Health Reference Level = percent of the total number of public water systems with at least one analytical result that
exceeded the MRL, !A Health Reference Level Health Reference Level, respectively
- % PWS Population Served with detections, % PWS Population Served >% Health Reference Level, % PWS Population Served > Health Reference Level = percent of the total population served
by PWSs with at least one analytical result exceeding the MRL, !A Health Reference Level, or the Health Reference Level, respectively
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Regulatory Determination Support Document for Aldrin and Dieldrin
July 2003
Figure 3-4:  States with PWSs with detections of dieldrin for all States with data in
SDWIS/FED (Round 2)
                                                  All States
                                                               Dieldrin Detections in All Round 2 States
                                                                ~\ States not in Round 2
                                                                ^| No data for Dieldrin
                                                                r] States with No Detections (No PWSs > MRL)
                                                                 States with Detections (Any PWSs > MRL)
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Regulatory Determination Support Document for Aldrin and Dieldrin
                                 July 2003
Figure 3-5:  Round 2 cross-section States with PWSs with detections of dieldrin (any PWSs
with results greater than the Minimum Reporting Level [MRL]; above) and concentrations
greater than the Health Reference Level (HRL; below)
                                          o
              * State of Massachusetts is an outlierwith 18.18% PWSs > MRL
Dieldrin Occurrence in Cross-section States
|    | States not in Cross-Section
|    | No data for Dieldrin
Id 0 00% PWSs > MRL
     0.01 - 1.00%  PWSs > MRL
      1.00% PWSs > MRL *
                                          O
 Dieldrin Occurrence in Cross-section States
     States not in Cross-Section
     No data for Dieldrin
 "^ 000% PWSs > HRL
     0.01 - 1.00% PWSs> HRL
      1.00% PWSs > HRL
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pressure (Black, 1974). Under conditions of longer-term exposure to lower doses of these
compounds, neurotoxic symptoms may also include headache, dizziness, general malaise,
nausea, vomiting, and muscle twitching or muscle spasms (Jager, 1970; ATSDR, 2000b).
Dieldrin exposure has been linked to two cases of immunohemolytic anemia, where an immune
system response destroys red blood cells (Hamilton et al., 1978; Muirhead et al., 1959), and
aldrin/dieldrin exposure has been linked with several instances of aplastic anemia, where bone
marrow cannot adequately regenerate red blood cells (de Jong, 1991; Pick et al., 1965; ATSDR,
2000b). However, at least some of these studies are problematic. In any case, hematological or
immunological (e.g., dermal sensitization) effects have not generally been found in humans
following exposure to either compound.

    Common acute or subchronic neurotoxic effects observed in animals are characterized by
increased irritability, salivation, hyperexcitability, tremors followed by convulsions, loss of body
weight, depression, prostration, and death (Borgmann et al., 1952; Walker et al., 1969; Wagner
and Greene, 1978;  Woolley et al.,  1985; NCI, 1978; Casteel, 1993). Manifestations of
hepatotoxicity (e.g., elevated serum enzyme levels, unregulated liver cell regenerations, rapid
turn-over in bile duct cells, localized cell degeneration and death, etc.) have been observed in
animals following subchronic-to-chronic exposure to moderate-to-high concentrations of
aldrin/dieldrin (summarized in  ATSDR, 2000b).  Relatively low-dose, chronic exposures to
either compound have been associated with changes in the tissue structure of the liver in rat
studies (e.g., Fitzhugh et al., 1964; Walker et al., 1969).  There is some evidence from animals
that aldrin/dieldrin exposure may either induce renal lesions or exacerbate pre-existing kidney
illness (ATSDR, 2000b; Fitzhugh et al., 1964; Harr et al., 1970).

    Various in vivo and in vitro studies have provided evidence that aldrin and dieldrin may act
as weak endocrine disrupters.  Changes in male and female hormone levels and/or receptor
binding, and degeneration of male germ cells and seminiferous tubules in the testes (the Ley dig
cell ultrastructure) have been observed.  In females, effects on the estrus cycle and rapid turnover
of breast cells  and of the cells lining the uterus have been reported (ATSDR, 2000b). Oral
administration of aldrin/dieldrin to maternal or paternal animals has produced somewhat
equivocal evidence of decreased fertility (Dean et al.,  1975; Epstein et al., 1972; Good and Ware,
1969; Harr et al., 1970; Virgo and Bellward, 1975), and  injection of aldrin in the abdominal
cavity has produced various adverse effects on the male  reproductive system (ATSDR, 2000b).

    Immunosuppression by dieldrin has been reported in a number of mouse studies
(Krzystyniak et al., 1985; Loose, 1982; Loose et al., 1981).  A number of long-term bioassay
studies have provided evidence that aldrin and dieldrin also cause liver cancer in mice (Davis
and Fitzhugh,  1962; Davis, 1965; Song and Harville, 1964; NCI, 1978; MacDonald et al., 1972;
Walker et al., 1972; Thorpe and Walker, 1973; Meierhenry et al., 1983). In one mouse study,
dieldrin was found to have induced lung, lymphoid and "other" tumors (Walker et al., 1972). In
contrast, neither compound has been found to induce liver tumors in rats (Treon and Cleveland,
1955; Song and Harville,  1964; Deichmann et al., 1967,  1970; Deichmann, 1974; NCI, 1978;
Fitzhugh et al., 1964; Walker et al., 1969),  although a number of these studies suffered from one
or more serious deficiencies.

    Despite some sporadic, statistically significant increases in rectal or liver/biliary cancer,
occupational and epidemiological studies have failed to provide any convincing evidence for the
carcinogenicity of either aldrin or dieldrin in humans (Van Raalte, 1977; Versteeg and Jager,
1973; de Jong, 1991; de Jong et al., 1997; Ditraglia et al., 1981; Brown, 1992; Amaoteng-
Adjepong et al., 1995).  In fact, the ratio of deaths in the exposed vs. general populations for
both specific causes and all causes of death have generally been less than 1.0.

    Not a great deal is known about the modes of action  that may underlie the various toxic
effects produced by exposure to aldrin or dieldrin.  The hyperexcitability associated with these

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compounds' neurotoxicity has generally been thought to arise from increased and unregulated
nerve impulses throughout the central nervous system, but whether this results from facilitated
neurotransmitter release at the nerve terminals, or from reducing the activity of inhibitory
neurotransmitters within the central nervous system, has been unclear (ATSDR, 2000b).
Mehrota et al.  (1988, 1989) have proposed that dieldrin may act by inhibiting a calcium-
dependent brain enzyme (ATPase), resulting in higher intracellular calcium levels that would
promote neurotransmitter release.  More recent work provides significant evidence  that aldrin
and dieldrin's principal mode of neurotoxic action likely involves their role as antagonists for the
membrane receptor for the inhibitory neurotransmitter, gamma aminobutyric acid (GAB A),
blocking the influx of chloride ion through the GABA-controlled channel (Klaassen, 1996;
Nagata and Narahashi, 1994, 1995; Nagata et al., 1994; Brannen et al., 1998; Johns et al., 1998;
Liu et al., 1997, 1998).  Additionally, at least one in vitro study using fetal rat brain cells
suggests that dieldrin may have an even greater functional effect on the nerve cells  that use
dopamine as a neurotransmitter (Sanchez-Ramos et al., 1998).

   Genotoxicity, defined as direct action of the chemical on the genetic material (i.e., DNA), is
not expected to have a predominant role in the mode of action for these compounds'
carcinogenicity.  The capacity of aldrin and dieldrin to inhibit various forms of in vitro
intercellular communication in both human and animal cells may be significant in triggering
tumor production due to cell proliferation, unregulated cell growth and premature cellular death
(Kurata et al.,  1982; Wade et al., 1986; Zhong-Xiang et al., 1986; Mikalsen and Sanner, 1993).
However, these growth effects are epigenetic: they are unrelated to any change in DNA.
Generally speaking, hepatocarcinogenic effects in mice may potentially be associated with
epigenetic modes of action, but not in rats.

4.2 Dose-Response Characterization and Implications in Risk Assessment

   In adult humans, the acute oral lethal dose for aldrin/dieldrin has been estimated at
approximately 70 mg/kg bw (Jager, 1970;  ATSDR, 2000b), which is about 3 times  the dose
reported to have induced convulsions within 20 minutes of ingestion (Spiotta, 1951).  The oral
dose that is sufficient to kill 50 percent of the treated animals (Oral LD50) was determined in
various  animal species for the two compounds; these values have been reported to range from
33-95 mg/kg bw, and appear to be affected by age at the time of exposure. In rats, LD50 values
were reported as 37 mg/kg bw for young adults, 25 mg/kg bw for two week-old pups, and a high
168 mg/kg bw for newborns (Lu et al., 1965).

   Meaningful dose-response relationships have not been adequately characterized in humans
for any of the toxic effects of aldrin or dieldrin. In animals, oral exposure to aldrin/dieldrin has
produced a variety of dose-dependent effects over a collective dose range of at least three orders
of magnitude (< 0.05-50 mg/kg bw), depending on the specific endpoint and the duration of
exposure (ATSDR, 2000b).  Dose-response information for some key chronic and cancer
bioassay studies are summarized in Table  9-1 of the Drinking Water Support Document for
Aldrin and Dieldrin (USEPA, 2001). For  noncancer effects, the USEPA has determined oral
Reference Doses (RfDs) for both aldrin and dieldrin based upon the most sensitive  relevant toxic
effects (critical effects) that have been  reported. The RfD is an estimate, with an uncertainty
spanning perhaps an order of magnitude, of a daily oral exposure to the human population
(including sensitive subgroups) that is likely to be without an appreciable risk of deleterious
effects during a lifetime.  For aldrin, the critical effect was liver toxicity observed in rats after
chronic  exposure to approximately 0.025 mg/kg bw-day, the Lowest Observed Adverse Effect
Level (LOAEL) and lowest dose tested (Fitzhugh et al., 1964).  This dose was divided by a
composite uncertainty factor of 1,000 (to account for rat-to-human extrapolation, potentially
sensitive human subpopulations, and the use of a LOAEL rather than a No Observed Adverse
Effect Level-NOAEL) to yield an oral RfD for aldrin of 3 x 10"5 mg/kg bw-day.  Similarly for
dieldrin, a chronic rat study NOAEL for liver toxicity of approximately 0.005 mg/kg bw-day

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Regulatory Determination Support Document for Aldrin and Dieldrin                             July 2003


(Walker et al., 1969) was divided by a composite uncertainty factor of 100 (to account for rat-to-
human extrapolation and potentially sensitive human subpopulations) to yield an oral RfD of 5 x
10"5 mg/kg bw-day.

   Based upon the mouse long-term bioassays discussed in section 4.1, the USEPA has
classified both aldrin and dieldrin as group B2 carcinogens under the current cancer guidelines
(USEPA, 1986), i.e., as probable human carcinogens with little or no evidence of carcinogenicity
in humans, and sufficient evidence in animals. Mechanistic studies performed in vitro and in
vivo suggest that one or more non-genotoxic modes of action may underlie or contribute to the
carcinogenic potential of aldrin and dieldrin, but these effects are not completely established, nor
can a role for genotoxic mechanisms confidently be eliminated based upon the available data.
Based upon these considerations, the quantitative cancer risk assessments of aldrin and dieldrin
have been conducted conservatively using the linear-default model.

   This approach has yielded geometric mean cancer potency estimates for aldrin and dieldrin
of 17 and 16 (mg/kg bw-day)"1, respectively. Using this potency, a concentration of one
microgram of aldrin or dieldrin in a liter of water may be associated with a theoretical cancer
risk of 4.9 deaths in a population of 10,000 for aldrin or 4.6 deaths for dieldrin, respectively. For
both compounds, a drinking water concentration of 0.002 |ig/L would lead to an estimated
increase in lifetime cancer risk of 10"6. This concentration, 0.002 |ig/L, was selected as the
Health Reference Level (HRL) for each chemical.  The HRLs are benchmark values that are
used in evaluating the occurrence data (section 3.3) while risk assessments for the contaminants
are being developed.

4.3 Relative Source Contribution

   Analysis of relative source contribution compares the magnitude of exposures  expected via
consumption of drinking water with those estimated for other relevant media such as food, air
and soil. The data summarized in section 3.3 provide the basis for estimating the amounts of
aldrin and dieldrin ingested via drinking water in exposed populations.  A less-conservative
estimate was achieved by utilizing the median and 99th percentile detected concentrations
derived from only Unregulated Contaminant Monitoring (UCM) Round 2 cross-section data,
which will certainly underestimate to some degree the true contribution of drinking water to the
exposed population's total intake of aldrin/dieldrin.

   For a 70 kg adult consuming 2 L/day of water containing aldrin at either 0.58 |ig/L (median
detect concentration) or 0.69 |ig/L (99th percentile detect concentration), the corresponding aldrin
intakes from drinking water are 1.7 x 10"5 and 2.0 x 10"5 mg/kg bw-day, respectively.  For a 10
kg child consuming 1 L/day of water, the comparable values are  5.8 x  10"5 and 6.9 x 10"5  mg/kg
bw-day.

   Similarly, for median and 99th percentile detected concentrations of dieldrin (0.16 and 1.36
Hg/L, respectively), the corresponding adult drinking water intakes of dieldrin are  0.46 x 10"5 and
3.9 x 10 mg/kg bw-day, respectively. Dieldrin drinking water intake values for the 10 kg child
are 1.6 x 10 and 14 x 10"5 mg/kg bw-day.

   Chapter 4.0 of the Drinking Water Support Document for Aldrin and Dieldrin  (USEPA,
2001) presents data on the estimated daily dietary intake of aldrin and dieldrin. Combining
estimates for non-fish food with those for fish and shellfish, adult and child dietary intakes of
aldrin are estimated at 3.3-6.5 x 10"5 and 13-18 x 10"5 mg/kg bw-day, respectively. For dieldrin,
the comparable adult and child dietary intakes are 3.6 x  10   and  14 x 10"5 mg/kg bw-day.

   Comparing these derived estimates for intakes via drinking water and diet, the ratios of
dietary intake to drinking water intake for aldrin range from 1.7 to  3.8  across all combinations of

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Regulatory Determination Support Document for Aldrin and Dieldrin                             July 2003


age and drinking water concentration level. For dieldrin, the food/water intake ratios for adults
and children are 0.9 and 1.0 using the 99th percentile water concentration, and 7.8 and 8.8 using
the median water concentration.  Applying the more conservative aldrin/dieldrin water
concentrations based upon the monitoring data of all reporting UCM Round 2 States would
reduce all of these food/water ratios by a factor of approximately 3 to 6. Thus, when
conservatively analyzed relative to the diet, drinking water could potentially be responsible for a
significant portion of total daily intake of aldrin/dieldrin, but only for limited populations under
exposure circumstances that are considered unlikely.

   The estimated daily intakes of aldrin and dieldrin from air for adults and children are small
(ranging from 0.013 x 10"5 to 0.24 x 10"5) relative to the unlikely, but potential, drinking water
intakes and dietary intakes discussed above. Although soil data were not available for aldrin,
data for dieldrin indicates that ingestion of soil represents only a minor exposure pathway for
these compounds.

4.4 Sensitive Populations

   The available literature did not provide direct evidence for any human subpopulations that
are particularly sensitive to the toxic affects of aldrin/dieldrin,  or for which the relevant
information on absorption, metabolism, or elimination of these chemicals are known to be
significantly different from those for the general population. Speculatively, fetuses and very
young children might be at increased risk from exposures to aldrin/dieldrin as a result of the
limited ability of the immature system to transform these contaminants in the liver to less toxic
chemicals that would be eliminated from the exposed individuals; and as a result would have a
higher vulnerability during these critical periods of development. Several mechanistic studies,
which describe the prenatal effects of aldrin/dieldrin on GAB A receptor malfunctions and on
subsequent behavioral impairment, may suggest an increased sensitivity of children (Brannen et
al., 1998; Liu et al., 1998; Johns et al., 1998; Castro et al., 1992). Declining organ  and immune
functions may also render the elderly more susceptible to aldrin/dieldrin toxicity. Additionally,
it is reasonable to expect that individuals with compromised liver, immune or neurological
functions (as a result of disease, genetic predisposition or other toxic insult) might also display
increased sensitivity to these compounds. However, no study has convincingly demonstrated
sensitivity of any one group.

4.5 Exposure and Risk Information

   Because the HRL of 0.002 |ig/L for these compounds is below the Minimum Reporting
Level (MRL), any recorded detection will be above all three reference levels (MRL, 1A> HRL,
HRL). Therefore, estimates of the national population exposed to concentrations greater than
any of these levels will be equivalent.  For aldrin, data from only the UCM Round 2 cross-
section (less-conservative approach or probable underestimate) indicate that about 39,000 people
are served by public water systems (PWSs) with detections greater than the MRL, !/2 HRL, and
HRL. Using the more conservative data from all reporting Round 2 UCM States (a probable
overestimate), approximately 1,052,000 people are served by systems with detections greater
than the MRL, 1A> HRL, and HRL.  The corresponding estimates for dieldrin are approximately
150,000 people and 793,000 people, respectively.

   For aldrin, the median and 99th percentile concentrations of detections based upon all Round
2 UCM data were 0.18 and 4.40 |ig/L, respectively.  Based only upon the 19-State Round 2
cross-section data, the corresponding values are 0.58 and 0.69  |ig/L. The respective two sets of
values for dieldrin are 0.42 and 4.40 |ig/L,  and 0.16 and 1.36 |ig/L.  While these values are
above the HRL of 0.002 |ig/L, it is necessary to consider that the corresponding values for all
samples were below the detection limit, and that the HRL itself is likely a very conservative
estimate of any human risk resulting from exposure to these chemicals.

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4.6 Conclusion

   In conclusion, while there is evidence that aldrin and dieldrin may have adverse health
effects in humans, including the potential to cause cancer, these chemicals are detected very
infrequently and generally at very low concentrations in drinking water.  Furthermore, there
should be no new releases to the environment because the compounds have not been used in the
United States since 1987. Therefore, it is unlikely that aldrin or dieldrin will occur at
frequencies or concentrations that are of public health concern or that regulation represents a
meaningful opportunity for health risk reduction in persons served by public water systems. All
CCL regulatory determinations and further analysis are formally presented in the Federal
Register Notices (USEPA, 2002a; 67 FR 38222; and USEPA, 2003a; 68 FR 42898).


5.0 TECHNOLOGY ASSESSMENT

   If a determination has been made to regulate a contaminant, SDWA requires development of
proposed regulations within two years of making the decision.  It is critical to have suitable
monitoring methods and treatment technologies to support regulation development according to
the schedules defined in the SDWA.

5.1 Analytical  Methods

   The availability of analytical methods does not influence EPA's determination of whether or
not a CCL contaminant should be regulated.  However, before  EPA actually regulates a
contaminant and establishes a Maximum Contaminant Level (MCL), there must be an analytical
method suitable for routine monitoring.  Therefore, EPA needs to have approved methods
available for any CCL regulatory determination contaminant before it is regulated with an
NPDWR.  These methods must be suitable for compliance monitoring and should be cost
effective, rapid, and easy to use.

   Aldrin and dieldrin are unregulated contaminants for which monitoring was required under
the Unregulated Contaminant Monitoring Program (USEPA, 1987; 52 FR 25690). Monitoring
for aldrin and dieldrin was initiated through rulemaking in 1991 (USEPA, 1991b; 56 FR 3526),
and began in 1993. The contaminants already have well-documented analytical methods
developed specifically for low-level drinking water analyses (see Table 5-1).

5.2 Treatment Technology

   Treatment technologies also do not influence the determination of whether or not a
contaminant should be regulated.  But before a contaminant can be regulated with an NPDWR,
treatment technologies must be readily available. EPA's Office of Research and Development
(ORD) has researched treatment technologies for all  of the organic compounds listed as
regulatory determination priorities on the CCL, including aldrin and dieldrin. The two
appropriate technologies reviewed were granular activated carbon (GAC) and air  stripping.

   Granular activated carbon treatment removes contaminants via the physical and chemical
process of sorption, by which the contaminants attach to the carbon surface as water passes
through the carbon bed.  Activated carbon has a large sorption  capacity for many water
impurities including synthetic organic contaminants, taste and  odor causing compounds, and
some species of mercury. Adsorption capacity is typically represented by the Freundlich
isotherm constants, with higher Freundlich (K) values indicating greater sorption potential.

   Air stripping involves the continuous contact of air with the water being treated, allowing
volatile dissolved contaminants to transfer from the source water to the air. After contact, the

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Regulatory Determination Support Document for Aldrin and Dieldrin
July 2003
"contaminated air" is swept from the system, taking the contaminant out of contact with the
treated water.  The driving force for the water-to-air transfer of the volatile contaminants is the
contaminant's concentration gradient between the water and air. The Henry's Law constant is a
commonly used indicator of the tendency of a  contaminant to partition from water to air.  A
larger Henry's constant indicates a greater
Table 5-1: Analytical methods for aldrin and dieldrin
Pethod
EPA 525.2
EPA 505
EPA 508
EPA 508.1
Type
Gas Chromatography
(GC)/Quadrupole
Mass Spectrometry
(MS)
GC/Ion Trap MS
GC/Electron Capture
Detectors (ECD)
GC/ECD
GC/ECD
Method Detection
Limit (jiig/L I'foj^
aldrin
0.11
0.045
0.075
0.014
0.009
Method Detection
Limit:{u.g/L)tor
dieldrin
0.053
0.11
0.012
0.011
0.003
equilibrium of the contaminant in the air.  Thus, contaminants having larger Henry's constants
are more easily removed by air stripping.

   Predictive computer modeling and specific chemical characteristics were used to determine
the isotherm constants needed to evaluate the two treatment technologies. The rule of thumb
used for SDWA compounds, learned through the development of cost-and-technology
documents to support other drinking water regulations, is that GAC is considered to be cost-
effective if the contaminant has a Freundlich (K) value above 200 (Speth and Adams, 1993). For
air stripping, a compound with a Henry's constant above dibromochloropropane (0.005) or
ethylene dibromide (0.037) is considered strippable at a reasonable cost.

   Since aldrin has a predicted Freundlich (K) value of 718,000, it can be effectively treated by
the GAC method. However, because its predicted Henry's Law constant is 0.027, aldrin can
only undergo effective air stripping procedures under certain concentration conditions.  Dieldrin
has a predicted Freundlich (K) value of 486,000 and a predicted Henry's Law constant of 2.0 x
10"5.  Therefore, only GAC is an applicable treatment technology for dieldrin. Its low
volatilization potential makes air stripping impractical.
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6.0 SUMMARY AND CONCLUSIONS - DETERMINATION OUTCOME

    Three statutory criteria are used to guide the determination of whether regulation of a CCL
contaminant is warranted: 1) the contaminant may adversely affect the health of persons; 2) the
contaminant is known or is likely to occur in public water systems with a frequency, and at
levels, of public health concern; and 3) regulation of the contaminant presents a meaningful
opportunity for health risk reduction for persons served by public water systems.  As required by
SDWA, a decision to regulate a contaminant commits the EPA to propose a Maximum
Contaminant Level Goal  (MCLG) and promulgate an NPDWR for the contaminant. A decision
not to regulate a contaminant is considered a final Agency action and is subject to judicial
review. The Agency can choose to publish a Health Advisory (a nonregulatory action) or other
guidance for any contaminant on the CCL that does not meet the criteria for regulation.

    The available toxicological data indicate that aldrin and dieldrin have the potential to cause
adverse health effects in humans and animals.  In humans, the most common manifestation of
acute aldrin/dieldrin toxicity is neurotoxicity to the central nervous system, including
hyperirritability, convulsions, and coma, in some cases followed by cardiovascular effects such
as unusually rapid beating of the heart and elevated blood pressure. In smaller doses over time,
aldrin and dieldrin may cause headache, dizziness, general malaise, nausea, vomiting, and
muscle twitching or muscle spasms. Aldrin and dieldrin toxicity may also be responsible for
reported cases of immunohemolytic and aplastic anemia. Indications of aldrin/dieldrin toxicity
in animal subjects include neurotoxicity, hepatotoxicity (e.g., elevated serum enzyme levels,
unregulated liver cell regenerations, rapid turn-over in bile duct cells, localized cell degeneration
and death), changes in the tissue structure of the liver, renal lesions and exacerbation of pre-
existing kidney illness. Aldrin and dieldrin appear to be weak endocrine disrupters, affecting the
reproductive system of animal subjects. Though their carcinogenicity in mice is established, no
occupational or epidemiological study has convincingly linked aldrin and dieldrin to cancer in
humans.

    Aldrin and dieldrin are synthetic organic compounds (SOCs) that have been used as
agricultural insecticides (primarily on corn and citrus products) and termite deterrents.
Production and most agricultural uses of aldrin and  dieldrin ceased in the U.S. in 1974, and all
uses and imports were discontinued in 1987.  The presence and persistence of aldrin and dieldrin
in the environment is evidenced by detections  of the compounds in hazardous waste sites in at
least 31 and 38 States, respectively (atNPL sites), as well as detections of both chemicals in site
samples in at least 40 States (listed in ATSDR's HazDat).

    In the ambient environment, aldrin and dieldrin  are occasionally detected at low
concentrations. Both substances are hydrophobic, and thus are more likely to sorb to  surface soil
or enter biotic tissue than enter groundwater aquifers. Aldrin has been detected more commonly
in streambed samples in agricultural land  use areas than in other land use areas or in biotic
tissue.  Dieldrin has been found to occur most commonly in agricultural surface waters and
shallow urban aquifers; it has also been detected in biotic tissue, suggesting a risk of
bioaccumulation.

    Monitoring data indicate that aldrin and dieldrin are infrequently detected in public water
supplies, with only 0.006% and 0.06% of all cross-section samples showing detections for aldrin
and dieldrin, respectively. Significantly, the values for the 99th percentile and median
concentrations of all cross-section samples are less than the Minimum Reporting Level (MRL)
for both contaminants. According to the cross-section model, less than 0.02% of the national
population served by public water supplies (40,000-50,000 people) is served by PWSs with
aldrin detections and less than 0.1% of the population (150,000 people) is served by PWSs with
dieldrin detections.  Using more conservative estimates of occurrence from all  States reporting
SDWA Round 2 monitoring  data, including States with biased data, those figures increase to

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Regulatory Determination Support Document for Aldrin and Dieldrin                             July 2003


only 0.5% of the PWS population served (approximately 1,052,000 people) for aldrin, and 0.4%
of the PWS population served (approximately 793,000 people) for dieldrin. (For details of the
methodology used to construct the national cross-section, see section 3.)

    Additional data from corn belt States, where use of aldrin and dieldrin was historically high,
were evaluated to supplement the cross-section data.  Drinking water data from Iowa, Indiana,
and Illinois also show low occurrence of aldrin and dieldrin.  There were no detections in either
surface or ground water PWSs in the State of Iowa.  Illinois and Indiana reported no
groundwater detections; surface water detections were low, with 1.8% of Illinois'  surface water
systems (0.1% of samples) showing detections of aldrin/dieldrin and 2.1% of Indiana's surface
water systems (0.3% of samples) showing  detections of dieldrin alone.  For Illinois and Indiana
surface water PWSs, the 99  percentile concentrations of all samples were below the reporting
level and the maximum concentrations were 0.1 |ig/L and 0.04 |ig/L, respectively.  Moreover, in
a survey of Illinois community water supply wells dieldrin  was detected in only 1.6% of all
sampled wells.

    EPA considers exposure to both the general public and  sensitive populations, including
fetuses, infants, and children, in making its regulatory determination. A factor often is included
in the reference dose to account for differences in sensitivity between human subpopulations.
Besides drinking water, food intake may also present a risk of exposure to aldrin and dieldrin, of
a similar order of magnitude, to both children and adults. (Exposure via air and soil are
considered less significant.)

    In conclusion, while there is  evidence that aldrin and dieldrin have adverse health effects in
humans, their occurrence in drinking water at frequencies or concentrations significant for public
health concern is low.  Furthermore, occurrence of aldrin and dieldrin in drinking water supplies
in the coming years is likely to decrease, since the substances are no longer produced or used
commercially. Therefore regulation of aldrin and dieldrin may be unlikely to represent a
meaningful opportunity for health risk reduction. All CCL regulatory determinations and further
analysis are formally presented in the Federal Register Notices (USEPA, 2002a; 67 FR 38222;
and USEPA, 2003a; 68 FR 42898).
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Regulatory Determination Support Document for Aldrin and Dieldrin                            July 2003


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Song, J. and W.E. Harville.  1964. Carcinogenicity of Aldrin and Dieldrin in Mouse and Rat
   Liver.  Fed. Proc. Fed. Am. Soc.  Exp. Biol.  23:336 (as cited in USEPA,  1987).

Speth, T.F. and J.Q. Adams. 1993.  GAC and Air-Stripping Design Support for the Safe
   Drinking Water Act.  In: Strategies and Technologies for Meeting SDWA Requirements.
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Spiotta, EJ. 1951. Aldrin Poisoning in Man. Arch. Ind. Hyg. Occup. Med.  4:560-566 (as cited
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Stevenson, D.E., E.F. Walborg, Jr., D.W. North, R.L.  Sielken, Jr., C.E. Ross, A.S. Wright, Y.
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   Environmental Components on Enzyme Function and Tumor Incidence in Livers of CFj
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USEPA.  1986.  Guidelines for Carcinogen Risk Assessment. Federal Register 51, no. 185  (24
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USEPA.  1987.  National Primary Drinking Water Regulations-Synthetic Organic Chemicals;
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USEPA.  1991b. National Primary Drinking Water Regulations - Synthetic Organic Chemicals
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USEPA.  1992.  Drinking Water; National Primary Drinking Water Regulations - Synthetic
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   106 (3 June): 38222.

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USEPA. 2002b.  Occurrence Estimation Methodology and Occurrence Findings Report for the
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Woolley, D., L. Zimmer, D. Dodge, and K. Swanson. 1985. Effects of Lindane-Type
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   2000).
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                     APPENDIX A: Abbreviations and Acronyms

ACGIH         - American Conference of Governmental Industrial Hygienists
ATSDR         - Agency for Toxic Substances and Disease Registry
CAS            - Chemical Abstract Service
CCL            - Contaminant Candidate List
CERCLA       - Comprehensive Environmental Response, Compensation & Liability Act
CMR           - Chemical Monitoring Reform
CWS           - community water system
DBCP          - dibromochloropropane
DNA           - deoxyribonucleic acid
BCD            - electron capture detectors
EHS            - extremely hazardous substance
EPA            - Environmental Protection  Agency
EPCRA         - Emergency Planning and Community Right-to-Know Act
FR             - federal register
GABA          - gamma aminobutyric acid
GAC           - granular activated carbon (treatment technology for organic compounds)
GC             - gas chromatography (a laboratory method)
g/mol           - grams per mole
GW            - ground water
HazDat         - Hazardous Substance Release and Health Effects Database
HEOD          - l,2,3,4,10,10-hexachloro-6,7-epoxy-l,4,4a,5,6,7,8,8a-octahydro-l,4-
                endo,exo-5,8-dimethanonaphthalene
HHDN          - 1,2,3,4,10,10-hexachloro-l,4,4a,5,8,8a-hexahydro-l,4-endo,exo-5,8-
                dimethanonaphthalene
HRL            - Health Reference Level
IOC            - inorganic compound
Koc             - organic carbon partition coefficient
Kow             - octanol-water partitioning coefficient
LD50            - 50% lethal dose
LOAEL         - lowest observed adverse effect level
MCL           - maximum contaminant level
MCLG          - maximum contaminant level goal
MDL           - method detection limit
mg             - milligrams
MRL           - minimum reporting level
MS             - mass spectrometry (a laboratory method)
NAWQA       - National Water Quality Assessment Program
NCI            - National Cancer Institute
NCOD          - National Drinking Water Contaminant Occurrence Database
NDWAC        - National Drinking Water Advisory  Council
NIOSH         - National Institute for Occupational  Safety and Health
NIRS           - National Inorganic and Radionuclide Survey
nm             - nanometer
NOAEL         - no observed adverse effect level
NPDWR        - National Primary Drinking Water Regulation
NPL            - National Priorities List
NTNCWS       - non-transient non-community water system
OGWDW       - Office of Ground Water and Drinking Water
OMB           - Office of Management and Budget
ORD           - Office of Research and Development
OSHA          - Occupational Safety and Health Administration
PWS            - public water system
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Regulatory Determination Support Document for Aldrin and Dieldrin
                                                              July 2003
RCRA
RfD
SARA Title III
SDWA
SDWIS
SDWIS/FED
SOC
SW
TPQ
TRI
UCM
UCMR
URCIS
USDA
USEPA
USGS
VOC
US
>MCL
>MRL
- Resource Conservation and Recovery Act
- reference dose
- Superfund Amendments and Reauthorization Act
- Safe Drinking Water Act
- Safe Drinking Water Information System
- Federal Safe Drinking Water Information System
- synthetic organic compound
- surface water
- threshold planning quantity
- Toxic Release Inventory
- Unregulated Contaminant Monitoring
- Unregulated Contaminant Monitoring Regulation/Rule
- Unregulated Contaminant Monitoring Information System
- United States Department of Agriculture
- United States Environmental Protection Agency
- United States Geological Survey
- volatile organic compound
- micrograms
- percentage of systems with exceedances
- percentage of systems with detections
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