United States
Environmental Protection
Agency
Office of Water
Office of Pesticides and
Toxic Substances
Fall 1990
National Pesticide Survey
Analytical Methods
How Were
Analytes
Selected?
Determining
Analytical
Methods
The U.S. Environmental Protection Agency (EPA) has completed its five-year
National Survey of Pesticides in Drinking Water Wells (NPS). A joint project of EPA's
Office of Drinking Water (ODW) and Office of Pesticide Programs (OPP), the Survey
was designed to assess the extent and severity of the presence of pesticides and
nitrate in drinking water wells nationwide, and the relationship of pesticide use and
ground-water vulnerability to the presence of pesticides and nitrate.
In designing the Survey, EPA selected chemicals (called Survey analytes) to test
for, and identified appropriate testing methods (called Survey analytical methods) for
the detection of these analytes. This fact sheet describes how EPA selected analytes,
identified analytical methods, and used the analytical methods in the laboratories.
EPA tested water samples from 783 rural domestic wells and 566 community
water system wells, nationwide, for the presence of 101 pesticides, 25 pesticide
degradates, and nitrate (a total of 127 Survey analytes). These analytes were chosen
by EPA from among approximately 600 pesticides registered for agricultural use by
EPA. EPA identified those that had:
chemical/physical properties, including water solubility, partition
coefficients, field half-life, and hydrolysis half-life that indicated a
potential to leach to ground water; and
• at least one million pounds or more of use nationwide in 1982.
EPA automatically selected all pesticides regulated by the Safe Drinking Water Act,
plus pesticides detected in ground-water studies done prior to the NPS.
EPA selected a final list of 127 analytes based on the criteria listed above for
which an analytical method existed or could be developed, plus other chemicals that
could be analyzed at the same time as the selected analytes that met the listed
criteria, without additional cost. The Survey Analytes Fact Sheet provides detailed
information on all Survey analytes.
Through extensive literature searches and consultation with scientific experts,
EPA identified existing laboratory methods for most of the analytes. Because of the
wide variety in procedures used in these methods and the large number of analytes to
be included in the Survey, EPA needed methods that could efficiently test for multiple
analytes. In the end, EPA selected two existing EPA methods (NPS Methods 7 and 9)
and developed six new methods (NPS Methods 1-6). One of the new methods tests
for ethylene thiourea and the other five, referred to as multi-residue methods, are each
capable of detecting ten or more analytes (NPS Methods 1-5). EPA dropped one
potential method (NPS Method 8). NPS Method 9 analyzes the combined presence of
nitrate and nitrite and expresses the result as nitrogen (N).
A short description of the eight analytical methods, which includes the type and
number of analytes, is presented in Exhibit 1.
WPS Analytical Methods
Printed on Recycled Paper
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Exhibit 1
Analytes Detectable By Method
NFS METHOD 1: Gas Chromatography with a Nitrogen-Phosphorous Detector
(46 Analytes)
Alachlor
Ametryn
Atraton
Atrazine
Bromacil
Butachlor
Butylate
Carboxin
Chlorpropham
Cycloate
Diazinon*
Dichlorvos
Diphenamid
Disulfoton*
Disulfoton sulfone*
Disulfoton sulfoxide*
EPIC
Ethoprop
Fenamiphos
Fenarimol
Fluridone
Hexazinone
MGK 264
Merphos*
Methyl paraoxon
Metolachlor
Metribuzin
Mevinphos
Molinate
Napropamide
Norflurazon
Pebulate
Prometon
Prometryn
Pronamide*
Propazine
Simazine
Simetryn
Stirofos
Tebuthiuron
Terbacil
Terbufos*
Terbutryn
Triademefon
Tricyclazole
Vernolate
NPS METHOD 2: Gas Chromatography with an Electron Capture Detector
4,4-DDD Dieldrin Heptachlor epoxide
4,4-DDE Endosulfan I Hexachlorobenzene
4,4-DDT Endosulfan II Methoxychlor
Aldrin Endosulfan sulfate Propachlor
Chtorobenzilate* Endrin Trifluralin
Chloroneb Endrin aldehyde alpha - HCH
Chlorothalonil Etridiazole beta - HCH
DCPA Heptachlor delta - HCH*
(29 Analytes)
gamma - HCH
alpha-Chlordane
gamma-Chlordane
cis - Permethrin
trans - Permethrin
NPS METHOD 3: Gas Chromatography with an Electron Capture Detector
2,4-D 4-Nitrophenol* Dalapon*
2,4-DB Acifluorfen* Dicamba
2,4,5-TP Bentazon Dicamba, 5-hydroxy-
2,4,5-T Chloramben* Dichlorprop
3,5-0!chlorobenzoic acid DCPA acid metabolites Dinoseb
(17 Analytes)
Pentachlorophenol (PCP)
Picloram
NPS METHOD 4: High Performance Liquid Chromatography with an Ultraviolet Detector
Atrazine, deethylated Diuron Metribuzin DA
Barfaan Fenamiphos sulfone Metribuzin DADK*
Carbofuran, phenol-3-keto- Fenamiphos sulfoxide Metribuzin DK*
Carbofuran, phenol Fluometuron Neburon
Cyanazine Linuron Pronamide metabolite
(18 Analytes)
Propanil
Propham
Swep
NPS METHOD 5: Direct Aqueous Injection HPLC with Post-Column Derivatization
Aldicarb Baygon Carbofuran, 3-hydroxy-
Aldicarb suifone Carbaryl Methiocarb
Aldtoarb sulfoxide Carbofuran Methomyl
(10 Analytes)
Oxamyl
NPS METHOD 6: Gas Chromatography with a Nitrogen-Phosphorous Detector
Ethylene thiourea (ETU)
(1 Analyte)
NPS METHOD 7: Microextraction and Gas Chromatography
Ethylene dibromide (EDB) 1,2 - dichloropropane**
Dibromochloropropane (DBCP) cis - 1,3 - dichloropropene**
(5 Analytes)
trans -1,3-
dichloropropene**
NPS METHOD 9: Automated Cadmium Reduction and Colorimetric Detection
Nilrate and nitrite measured as nitrogen (N)
(1 Analyte)
* Qualitative only.
** Method 8 dropped. Analytes previously included in Method 8 also detectable by Method 7.
WPS Analytical Methods
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In the
Laboratory
Laboratory
Analysis
Completed
Where to Go
for More
Information
EPA contracted with five laboratories to perform one or more of the NPS
analytical methods. Two EPA laboratories managed the contracts with the contract
laboratories, provided technical support, reviewed the data from the laboratories and
carried out referee analyses. A third EPA laboratory provided laboratory analysis
support. In addition to the quality assurance procedures carried out by the contract
laboratories, the EPA laboratories analyzed duplicate samples for approximately 10
percent of the field samples collected, depending on the analytical method. In this
way, EPA ensured the accuracy of results.
Rigorous quality control (QC) procedures were followed throughout the Survey.
All positive detections of analytes using a gas chromatograph (GC) column (NPS
Methods #1,2,3,6 and 7) were confirmed by reanalyzing samples using a gas
chromatograph/mass spectrometer (GC/MS) or a different quantitative and qualitative
high performance liquid chromatographic (HPLC) column (NPS Methods 4 and 5).
Some GC/MS confirmations were performed by the contract laboratories; however, the
majority were performed by the EPA laboratories.
The manner in which a positive detection was reported was based on the
minimum quantification limit (MQL) for the analyte. The MQL is a measure of the
accuracy of the analytical instrumentation and methods used to detect the analyte and
below which the detected concentration is not considered reliable. Detections
between one-half the MQL and the MQL indicate that an analyte was present but were
reported without a concentration. A concentration could be determined for 112 of the
analytes above the reporting limit. The remaining 15 were difficult to quantify or to
determine a concentration level with any reliability. The Agency chose to go ahead
and look for the presence of these analytes and only report them as "positive
detections."
The laboratories performed a variety of QC procedures to eliminate, as much as
possible, the occurrence of false negative or false positive results. These procedures
included the use of laboratory and instrument control standards, analysis of method
blanks (a portion of reagent water analyzed as if it were a water sample) and analysis
of shipping blanks (reagent water transferred to a sampling bottle, shipped to the field,
and returned to the laboratory with the samples). QC analyses enabled EPA to
identify any problems with the laboratory methods or instrumentation that might affect
the accuracy and precision of the results, so that they could be quickly resolved.
EPA sampled over 1300 community water system wells and domestic drinking
water wells nationally from April 1988 to February 1990. Laboratory analysis was
completed in May 1990. EPA's Phase I Report on the Survey findings was released in
Fall 1990. A Phase II Report, including relational analyses, is scheduled for release in
Spring 1991.
This fact sheet is part of a series of NPS outreach materials, fact sheets and
reports. The following additional fact sheets are available through EPA's Public
Information Center (401 M Street SW, Washington DC 20460, 202-382-2080):
Project Summary
Glossary
Fact Sheet for each
detected analyte
Survey Design
Summary Results
How EPA Will Use
The NPS Results
Survey Analytes
Quality Assurance/
Quality Control
NPS Analytical Methods
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Additional information on the Survey and on pesticides in general can be
obtained from the following sources:
U.S. EPA Safe Drinking Water Hotline
1-800-426-4791 (In Washington, DC - 382-5533)
Monday-Friday, 8:30 am to 4:30 pm Eastern Time
National Pesticide Telecommunications Network
1-800-858-7378
24 hours a day
U.S. EPA Office of Pesticide Programs (OPP) Docket
401 M Street, SW Room NEG004
Washington, DC 20460
(202) 382-3587
National Technical Information Service (NTIS)
5285 Port Royal Road
Springfield, VA 22161
(703) 487-4650
Information on regulation of
pesticides in drinking
water
Information on health
effects and safe
handling of pesticides
Background documents
for Survey (available
for review)
Copies of the
NPS Phase I Report
(available 1991) and
NPS Phase II Report
(when available)
If you are concerned about the presence of pesticides and nitrate in your private water
well, contact your local or State health department. Other experts in your State
environmental agency or agriculture and health department may also be helpful to
you. If you receive your drinking water from a community water system and have
questions about your water quality, contact your local community water system
owner/operator or the State water supply agency.
WPS Analytical Methods
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