Chlordane movement during rainfall
Abstract
Indoor rainfall simulation experiments were conducted to quantify the mass of technical chlordane leaving an experimental soil box in runoff, splash and leachate. The initial mass of technical chlordane was uniformly distributed throughout the soil at concentrations equal to those recommended for termite control around basement and foundation walls. Two silt loam soils and one sandy soil were studied. The mass of chlordane in runoff adsorbed to organic matter was estimated to be 16 times the mass of chlordane in runoff adsorbed to clay. For a soil with a clay-to-organic-matter ratio as high as 66, the mass of chlordane in runoff appears to be predominantly a function of clay content. For a soil with a clay-to-organic-matter ratio as low as 2 to 5, the mass of chlordane in runoff appears to be predominantly a function of organic matter content. An increase in rainfall intensity from 51 to 102 mm/hr increased chlordane mass in runoff by 300 to 500 percent. This increase in rainfall intensity increased the chlordane-to-sediment mass ratio in the runoff by 7 to 18 percent. The chlordane mass in runoff was 5 to 9 times as great as the mass of bromide in runoff. The chlordane mass in splash was 25 percent of the chlordane mass in runoff. Only the sandy soil at the higher rainfall intensity produced leachate. The chlordane mass in this leachate during the rainfall period was 37 percent of the chlordane mass in runoff and 264 percent of the chlordane mass in splash. The total chlordane mass which left the soil box by runoff, splash and leachate was equivalent to 4 to 44 mg per square foot of treated surface. This amounted to 0.03 to 0.31 percent of the original chlordane mass applied to the experimental soil box. This could potentially occur from previous legal surface applications in agriculture and turf management, from more recent illegal surface applications in agriculture and turf management, from proper use (according to label directions) as a subsurface termiticide but where depth of untreated cover soil was insufficient, from improper use as a subsurface termiticide where treated soil remained uncovered at the surface or from disturbance by new construction of large areas treated in previous years. This type of horizontal movement of chlordane and other organochlorine pesticides has been documented. Bennett et al. (1974) measured 70 ppb of gamma chlordane in the top five inches of soil located 10 feet away from a foundation wall treated 21 years earlier. Lichtenstein (1958) found higher concentrations of the organochlorine insecticides aldrin, lindane and DDT on the downslope side than on the upslope side of treated test plots. Similarly, Peach et al. (1973) found surface movement of aldrin, lindane and heptachlor toward points of lower elevation in a sloping field. Haan (1971) conducted laboratory rainfall-runoff experiments following surface treatment with aldrin, dieldrin and DDT and found that sediment carried more than twice as much pesticide mass as the water. Wauchope (1978) reviewed the literature on pesticide losses in runoff water from agricultural fields. He found that organochlorine pesticides lose about 1 percent of the total mass applied to the field through runoff. This compared to other commercial pesticides which lose 0.5 percent or less unless severe rainfall conditions occur within 2 weeks after application. Another important consideration is the mass of pesticide located within a few millimeters of the soil surface. Investigators have found that it is this zone from which pesticides are released during rainfall. Sharpley (1985) studied 5 soils and found the depth of this zone to range from 2 to 4 mm for 4 percent slopes under 50 mm/hr rainfall intensity to 13 to 37 mm for 20 percent slopes under 160 mm/hr rainfall intensity.