United States
                 Environmental Protection
                 Agency	
                      Pesticides And
                      Toxic Substances
                      (7508W)	
738-F-91-107
September 1991
                 R.E.D.   FACTS
     Pesticide
Reregistration
   Use Profile
Silicon  Dioxide  and


Silica  Gel	

     All pesticides sold or used in the United States must be registered by
EPA, based on scientific studies showing that they can be used without
posing unreasonable risks to people or the environment. Because of
advances in scientific knowledge, the law requires that pesticides which
were first registered years ago be reregistered to ensure that they meet
today's more stringent standards.
     In evaluating pesticides for reregistration, EPA obtains and reviews a
complete set of studies from pesticide producers,  showing the human health
and environmental effects of each pesticide.  The Agency imposes any
regulatory controls that are needed to effectively manage each pesticide's
risks.  EPA then reregisters pesticides that can be used without posing
undue hazards to human health or the environment.
     When a pesticide is eligible for reregistration, EPA announces this and
explains why in a Reregistration Eligibility Document, or RED.  This fact
sheet summarizes the information in the RED for silicon dioxide and silica
gel.

     Silicon dioxide and silica gel are insecticides and acaracides, used in
controlling insects, mites and ticks in a variety of indoor and outdoor sites.
Silicon dioxide dust is applied with a hand-held or power duster to stored
grain, other food, feed and ornamentals; in food handling areas;  and on pets
and their living/sleeping quarters.  Silica gel dust or pressurized liquid is
applied by hand-held power duster, aerosol can or injection into cracks and
crevices.  Silica gel is used to control target pests in stored grain  crops, food
handling  areas, hospitals, sewage systems, and on animals/pets and their
living quarters.
     Silicon dioxide is diatomaceous earth, a naturally-occurring material
composed of the shells of minute, single-celled algae. Silica gel is an
amorphous form of silicon dioxide. Both employ a physical mode of action
to control insects.  They are abrasive and act as desiccants, removing the
oily, protective film that covers insects' bodies, causing them to dry out and
die.

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    Regulatory
         History
Human Health
  Assessment
      Silicon dioxide and silica gel were first registered as pesticides in 1960
and 1956, respectively.  Currently, 18 registered pesticide products contain
silicon dioxide and 55 contain silica gel, usually in combination with other
active ingredients.  Because of their low toxicity when ingested, silicon
dioxide and silica gel have been exempted from tolerance, or legal residue
limit, requirements (please see Dietary Exposure,  below).

Toxicity
      Available studies demonstrate that silicon dioxide and silica gel have
moderate to low acute toxicity.  These pesticides have been placed in
Toxicity Category III for acute oral and dermal effects (Toxicity Category I
indicating the highest degree of toxicity, and IV the lowest).  Similarly, an
inhalation study  and eye and dermal irritation studies suggest moderate to
low toxicity.
      With regard to subchronic and chronic effects, crystalline silicon
dioxide has long been associated with silicosis, a progressive lung disease
which may result in lung cancer in humans.  However, amorphous silicon
dioxide (used in  pesticide formulations)  has not been associated with
silicosis.  The International Agency for Research on Cancer (IARC)
conducted an in-depth evaluation of the potential carcinogenicity of silicon
dioxide.  They found that there is  inadequate evidence to link amorphous
silica with  cancer effects in humans or  test animals.
                    Dietary Exposure
                          People may be exposed to silicon dioxide and silica gel through their
                    diets, since these pesticides may be applied to certain crops and used in and
                    around food handling and preparation areas. However, due to their
                    negligible toxicity, silicon dioxide and/or silica gel have been exempted
                    from the requirement of a tolerance, or legal residue limit, when applied to
                    growing crops and raw agricultural commodities after harvest (40 CFR
                    180.1001 (c) and (d)); to animals (40 CFR 180.1001 (e)); to growing crops,
                    raw  agricultural commodities after harvest, and animals (40 CFR
                    180.1017); and in food and feed processing and storage areas (40 CFR
                    185.1700 and  186.1700).  Both silicon dioxide and silica gel are  Generally
                    Recognized as Safe, or GRAS, as food additives (21 CFR 182.90 and
                    182.1711).
                    Applicator Exposure
                          People may inhale particles of silicon dioxide and silica gel when
                    applying these dust, aerosol, or crack-and-crevice injection formulations.
                    Current product labels for dust formulations require the use of a dust mask
                    for prolonged periods of use.   EPA believes that applicators' dermal
                    exposure to these products also may be significant. However, since
                    applications and exposures normally occur only several times a year (or

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                         less) , the Agency is not requiring additional protective clothing or other
                         changes in use, at this time.

                         Human Risk Assessment
                               EPA concludes that the human health risk from exposure to silicon
                         dioxide and silica gel is low  and not unreasonable.  These pesticides are of
                         moderate to low acute toxicity.  Dietary exposure is believed to be
                         insignificant from a toxicological standpoint.  Applicator exposure may be
                         significant for each application, however,  these products generally are used
                         infrequently.
                               All environmental fate and ecological effects data requirements for
       Assessment  silicon dioxide and silica gel have been waived, as explained below.
                         Environmental Fate
                               Silicon dioxide consists of diatomaceous earth, a naturally-occurring
                         material.  Its primary component, silica, is found in common minerals like
                         quartz, sand and agate.  Silica gel is simply an amorphous form of silicon
                         dioxide.  These materials are ubiquitous, and unlikely to react chemically
                         with any other substances in the environment.
                         Ecological Effects
                               Silicon dioxide and silica gel are naturally-occurring, ubiquitous, and
                         chemically unreactive in the environment.  There is no evidence to suggest
                         that the use of these materials as pesticides, in accordance with approved
                         labeling, presents a hazard to nontarget organisms or the environment.

    Additional Data        While the generic data base for silicon dioxide and silica gel is
                         complete, product-specific product chemistry data are required for
                         reregistration, as specified in the Data Call-in Notice issued in  conjunction
                         with the RED.
  Product Labeling
Changes Required
     The labels of end-use products containing silicon dioxide and silica gel
must comply with EPA's current pesticide labeling requirements.  Any
product label that allows both manufacturing and end use must be amended
to specify one use or the other.
     In addition, product labels must specify the active ingredient
concentration as a percentage if solid, or in pounds per gallon if liquid. The
application rate, maximum number of applications, and the pre-harvest
interval also must be included. All sites where application is permitted must
be listed.
         Regulatory
         Conclusion
           Registered pesticide products containing silicon dioxide and
           silica gel can be used without causing unreasonable adverse

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                            effects in people or the environment. Therefore, they are
                            eligible for reregistration.
                           End-use products containing silicon dioxide or silica gel as the
                            sole active ingredient will be reregistered once product-specific
                            data and amended labeling are received and accepted by EPA.
                           End-use products containing silicon dioxide or silica gel in
                            combination with other active ingredients will be reregistered
                            once product-specific data and amended labeling are received
                            and accepted by EPA,  and when the  other active ingredients in
                            these products also are eligible for reregistration.

   For MOTG         EPA is requesting public comments on the Reregistration Eligibility
Information   Document for silicon dioxide and  silica gel during a 60-day  time period, as
                 announced in a Notice of Availability published in the Federal Register. To
                 obtain a copy of the RED or to submit written comments, please contact the
                 Public Response and Program Resources Branch, Field Operations Division
                 (7506C), Office of Pesticide Programs (OPP), US EPA, Washington, DC
                 20460, telephone 703-557-2805.
                       In the future, the RED will be available from the National Technical
                 Information Service (NTIS), 5285 Port Royal Road, Springfield, VA
                 22161, telephone 703-487-4650.
                       For more information about silicon dioxide and silica gel, or about
                 EPA's pesticide reregistration program, please contact  the Special Review
                 and Reregistration Division (7508W),  OPP, US  EPA, Washington, DC
                 20460, telephone 703-308-8000.  For information about reregistration of
                 individual silicon dioxide and silica gel products, please contact the
                 Registration Division (7505C), OPP, US EPA, Washington,  DC 20460,
                 telephone 703-557-5447.
                       For information about the health effects of pesticides,  or for assistance
                 in recognizing and managing pesticide poisoning symptoms, please contact
                 the National Pesticides Telecommunications Network (NPTN).  Call toll-
                 free 1-800-858-7378, 24 hours a day, seven days a week, or Fax your
                 inquiry to 806-743-3094.

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