Additional Reading

http://extoxnet.orst.edu/
The EXtension TOXicology NETwork, good general information - look under Toxicology Information Briefs - search and browse
Also have good information on specific pesticides

http://ca.water.usgs.gov/pnsp/index.html
USGS National Pesticide Synthesis, read the Quality of Our Nations Water section on pesticides

http://ca.water.usgs.gov/pnsp/atmos/atmos_9.html
Pesticides in the Atmosphere

Pesticides
What is a Pesticide?
Historical Use
Patterns of Use
Compound Types
Toxicology
Pesticide Studies, databases
Pesticides in Atmosphere, Surface water, Groundwater - occurrence, spatial distribution, temporal trends
Laws
Management

What is a Pesticide?
A pesticide is any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest. Pests can be insects, mice and other animals, unwanted plants (weeds), fungi, or microorganisms like bacteria and viruses. Though often misunderstood to refer only to insecticides, the term pesticide also applies to herbicides, fungicides, and various other substances used to control pests. Under United States law, a pesticide is also any substance or mixture of substances intended for use as a plant regulator, defoliant, or desiccant.

First generation pesticides: sulfur, tobacco, lead, arsenic, mercury compounds
Second-generation pesticides - synthetic organics, DDT etc
Chlorinated hydrocarbons -DDT, etc. - these types bio-accumulated
1970s-80s - move into triazines, carbamates, organophosphates, persistence, breakdown
1990s - low-use, sulfonylurea, sulfonamide, imidazolinone (Pinnacle, Accent, Pursuit, Scepter)

Table 3.6 Use and detections (Handout)
What are the main insecticide types in use in 1988 for ag, for home and garden?
What are the main herbicide types in use?

Between 1966 and 1988 how have use patterns changed? What compounds decreased, which increased, stayed the same?

Patterns of Use
What are the top three crops in terms of use for: herbicides and insecticides?

Where in the US are these types of pesticides used most?

Besides the main categories, what else are pesticides used for?

Toxicology
Chlorinated hydrocarbon pesticides
Lipid soluble, bioaccumulate
Many are carcinogenic

Primary irritant dermatitis
Allergic contact dermatitis
Photosensitization dermatitis

Pyrethroid Insecticides
Natural and synthetic analogues
Potential neurotoxins with large doses
Fairly safe at low doses

Physical, Chemical, and Biological Processes that Affect Distribution
SourcesPoint versus non-point sources
Quasi-point sources

Groundwater Processes

Advection
Hydrodynamic dispersion
Preferential flow
A growing body of evidence suggests that the consensus laboratory scale model of solute movement, the advection-dispersion equation, may not correctly describe field-scale chemical mobile movement near the soil surface
Preferential flow often associated with macropores - roots, burrows, wormholes
Also found in fractures in clayey soils
However studies have also found evidence for preferential flow in sandy soils with no visible evidence of fracturingSolute portioning - solid, aqueous, vapor phases

Most pesticides are organics, thus have some affinity for organic matter in the subsurface ("like attracts like")
· Hydrophobic or hydrophilic
Organochlorines were strongly hydrophobic

Other Processes/Practices that affect Distribution and Occurrence of Pesticides in GW
Climate/Recharge volumeThe climate of the area usually determines the crops grown and the types of pests present. The temperature and the intensity of the sun often determine the persistence of pesticide compounds. The frequency and duration of rainstorms may influence the degree to which pesticides are transported away from site of application.

Soil Factors
The tendency for pesticides to leach or be removed in surface runoff is mainly a function of the soil composition. Sandy soils drain rapidly and thus are susceptible to leaching problems. Clayey soil is less porous, so water will pool at the soil surface and run off instead of infiltrating.

Leaching more likely to occur in coarse, highly permeable, organic-carbon poor soils than in fine-textured, less permeable, organic-rich soils.

Hydrogeologic Setting
Higher in unconsolidated than in bedrock (Midwest), contradicted in Maine
Higher levels of metabolites in shallow S&G aquifers indicates either rapid recharge and/or shorter travel paths.
Decreased detections as overburden thickness increased
The lower the near-surface permeability, the less likely detections
Increase in areas of extensive fracturing, especially karstDepth to water table, a few showed strong correlation, many did not
Depth of well screen below the water table, again ambiguous results
Effects of surface water recharge (high correlation in ag areas, some dilution in other areas)

Well effects
Grouting
Large diameter shallow wells
(Some have claimed this is only reason why pesticides occur in GW)
High pumping rates
Well age (correlated with construction)

Pesticide Occurrence
Many studies

StudyDesign
Compounds analyzed for
Analytical detection limits
Targeted versus random sampling
Degree of public attention/funding for studies

Pesticide Studies, databases
Reviews of pesticide occurrence in groundwater, 1 70s, 20 80s, 11 90s
Monitoring and process studies cover scales from multi-state, single-state, local, field-scale, to batch reactor lab experiments.
Most field studies concentrate on depth of leaching, concentrations, metabolites for specific compounds and often are not comprehensive enough to be useful as an analysis of causal factors. Thus it is difficult to transfer results to other environmental settings For instance it can be difficult to distinguish transport processes from transformation processes in the field.

NAQWA results

Pesticides in the tmosphere

Laws

Management
Organic
IPM