Student Research: Gary Palcisko
Acid lead arsenate (PbHAsO4) was the primary insecticide used to control the codling moth in Washington fruit orchards between 1905 and 1947 (Benson, 1968; Peryea, 1991). Lead arsenate solution was sprayed directly onto the trees using hand sprayers. Excess spray dripped from the trees contaminating soils beneath or near them. The extent to which soil was contaminated depended on the application rate and the number of years that lead arsenate was applied. Application rates increased with time as the codling moth became more tolerant to the pesticide. Assuming that an orchard was active between 1905 and 1947 and that average application rates and formulations were used (see Figure 1), then 1850 pounds of arsenic and 5040 pounds of lead were applied per acre over those 43 years.
Use of lead arsenate dropped drastically in 1948 when DDT became widely available. High levels of arsenic in soil resulting from lead arsenate use rendered much of the land in central Washington unproductive for agriculture. Potential concern for human health arose when old orchard lands began to be converted to other land use purposes such as schools or residential areas. Lead and arsenic, the primary constituents of lead arsenate pesticide, are highly toxic to humans.
Taken from the beginning of thesis.