Dynamics of organochlorine pesticides in soils from a southeastern region of Argentina.

Monitoring of organochlorine pesticides (OCPs) was carried out to identify and quantify the contribution of point and nonpoint sources to the total OCP flux in a southeastern region of Argentina. Natural, recreational, and agricultural soils located in the surrounding of a lagoon were analyzed by gas chromatography with electron-capture detector. Physical and chemical characteristics (texture, humidity, and organic matter content) were determined at different depths (0-15 cm, 15-30 cm, and 45-55 cm). The pattern of OCP distribution was similar in all soil sampled, with DDT and metabolites > hexachlorocyclohexanes (HCHs) > heptachlor > chlordanes. The highest values of OCPs (656.1 ng/g dry wt) were found in the surface natural soil despite its never having received direct OCP application. This would be mainly due to the high organic matter content of the surface natural soils as well as its topographic position (highland hills), with main winds arriving from agricultural areas. Microorganism abundance and edaphic biota in the upper layer would justify the high levels of metabolites found. The agricultural soil (intensive tillage) also showed the highest OCP values (30.19 ng/g dry wt) in the surface horizon. Because of management practices, volatilization could have been one of the major causes of pesticide loss from this target area. Recreational soil showed the lowest OCP levels in the surface layer because of weathering that occurs when the nearby lagoon floods this zone. Our results show that, although most of these pesticides are banned, they are present in these soils and the atmospheric transport and deposition would be the major processes for distributing OCPs from target to natural areas.