In contrast to fertilizers, pesticides are usually insoluble in water and 

 reach waterways or groundwater by erosion, sedimentation, leaching through 

 soil, or by spilling. They degrade water quality and can be toxic to aquatic 

 organisms. The movement of pesticides on cropland is generally horizontal 

 rather than downward through the soil profile. Thus, the greatest threat of 

 pesticides is to surface water, although groundwater can be affected also. An 

 extended period of precipitation is needed to move pesticides deep into soil, 

 and it is unusual to find pesticides in the soil below 2 feet (0.6 m) . Local 

 groundwater contamination may result from improper disposal of pesticide 

 containers. Pesticides from containers buried in landfills sometimes seep 

 into groundwater. 



A study on nonpoint agricultural pollution (U.S. Soil Conservation Service 

 1979) identified the watersheds of the Pleasant, Narraguagus, and Harrington 

 Rivers as susceptible to contamination by chemical pollutants. These rivers 

 drain the blueberry barrens in the southeast corner of Washington County 

 (regions 5 and 6). Schoodic Lake, a shallow spring-fed kettlehole lake in the 

 middle of the barrens, is vulnerable to any contamination that may occur 

 within its drainage area. 



Little is known of the amounts of pesticides and defoliators that reach water 

 bodies in coastal Maine. Borns and coworkers (1971) showed that pesticide 

 levels in the groundwater supply in the Cherryfield area (region 5) after the 

 blueberry fields had been treated often have approached the maximum limits for 

 human consumption. Pesticides readily enter the groundwater supply through 

 the porous glacial till. This condition is most serious when heavy rains 

 follow pesticide applications. 



During the last 10 years, a change has taken place from long-lasting 

 hydrocarbon pesticides (organochlorines) to more toxic but shorter-lived 

 pesticides (carbamates and organophosphates) that are known to have fewer 

 residual effects. This change, together with improved pesticide management 

 practices, has resulted in fewer fish kills. The latter fact may indicate 

 that direct environmental effects are being reduced. 



The most visible result of pesticide contamination is fish and songbird 

 mortality. Fish kills are often the result of high concentrations of 

 chemicals entering a water body within a short period of time. They also can 

 occur after a rainfall that has been preceded by pesticide application, or 

 when chemicals are spilled or are sprayed into water accidentally. Songbird 

 dieoffs occur when pesticides with high bird toxicity are applied, 

 particularly when they are applied aerially. Examples are diazinon, fenthion, 

 carbofuran, and parathion. 



Pesticides also may have a more subtle effect on aquatic ecosystems if present 

 at low levels for long periods of time or if frequent contamination occurs. 

 Fish behavior and reproduction may be affected by chronic toxicity. The 

 behavior and reproduction of insectivorous songbirds (95% or more of coastal 

 Maine breeding birds) may be affected by chronic toxicity and by severe 

 decreases in insect populations. Canopy-feeding species are generally the 

 most vulnerable. The effects of pesticides on songbirds are discussed in 

 chapter 16, "Terrestrial Birds." Biological magnification may occur with some 

 persistent pesticides, such as organochlorines, which degrade at a slow rate 

 and become concentrated in the tissues of organisms high in the food chain. 



3-12 



