Clay soils, chlordane residues

The half-life of chlordane in soil is approximately 4 years. Residues of this highly persistent chemical have been found in excess of 10% of the initially applied amount 10 years or more after application. Chlordane does not chemically degrade nor does it biodegrade in soils. Chlordane binds rapidly to soil particles and stays adsorbed to clay soil. Combined with its insolubility in water, this produces a low potential for ground water contamination. Sandy soil, on the other hand, allows chlordane to pass into ground water. 

Chlordane and heptachlor residues from clay soils from houses constructed with crawl spaces are shown in Table I. Concentrations varied widely. The average level of chlordane in the first 10 cm of soil was 1405-ppm (15 samples) and the average concentration in soil from the 10 to 20 cm depth was 806 ppm (7 samples). In many instances) it was impossible to obtain a 10 to 20 cm depth sample, because of the hardness of the soil, interfering foundation footings, or construction debris which had been buried under many of the dwellings. The amount of heptachlor found in the soil samples averaged 386 ppm from the 0 to 10 cm (11 samples) and 261 ppm from the 10 to 20 cm depth (3 samples). 

Residues of chlordane and heptachlor in air from houses with crawl spaces constructed on clay soils are shown in Table II. The highest chlordane residues found were in the crawl space (8.7 pg/nP) compared to the kitchen (2.3 pg/m ) and bedroom (2.5 pg/m3), Heptachlor residues in air averaged 1.7 pg/m in crawl spaces compared to 0.6 pg/m3 in kitchens and bedrooms. 

Tables III and IV show residue levels of chlordane and heptachlor in soils and air, respectively, from crawl-slab constructed houses built on clay soils. Soil residues of chlordane averaged 1545 ppm (15 samples) from the 0 to 10-cm depth and 861 ppm (five samples) from the 10 to 20 cm depth. Heptachlor levels for the upper and lower soil layers were, respectively 441 ppm (11 samples) and 314 ppm (two samples). As was seen in crawl-space dwelling on clay soils, residues of chlordane were highest in air of the crawl space...

Table I. Chlordane and Heptachlor Residues in Clay Soils from Houses...

Few data are available on soil and airborne residues of chlordane and heptachlor from homes treated by commercial pest control firms. Thus, a study was undertaken to determine chlordane and heptachlor residues in clay and sand soils and in the air of selected houses. 

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