title: Soil-air exchange of organochlorine pesticides in the Southern United States.
abstract: Soil samples were collected from 30 farms in Alabama, Louisiana and Texas during 1999-2000 to determine residues of organochlorine pesticides (OCPs). One or more of the DDT compounds (p,p'-DDT, o,p'-DDT, p,p'-DDD, p,p'-DDE, o,p'-DDE) was above the quantitation limit (0.1 ng g(-1) dry weight) in every soil, and toxaphene was above the quantitation limit (3 ng g(-1)) in 26 soils. Chlordanes, dieldrin and hexachlorocyclohexane (HCH) isomers occurred less frequently (quantitation limits 0.1 ng g(-1) for dieldrin and 0.05 ng g(-1) for chlordanes and HCHs). OCPs were measured in air at 40 cm above the soil at selected farms to investigate soil-air partitioning. Concentrations of OCPs in air were positively and significantly (P<0.001-0.004) correlated to soil concentrations for toxaphene, p,p'-DDT, o,p'-DDT, p,p'-DDE, dieldrin, and trans-nonachlor. The regression was weaker (P=0.022) for cis-chlordane and not significant for trans-chlordane (P=0.43) nor gamma-HCH (P=0.80). Approach to soil-air equilibrium was assessed by calculating fugacities in the soil and air (f(s) and f(a)) for samples with quantifiable residues in both compartments. The fugacity fraction f(s)=0.5 at equilibrium and is <0.5 or >0.5 for net deposition and net volatilisation, respectively. Fugacity fractions varied greatly for different soil-air pairs, reflecting generally disequilibrium conditions. Mean fugacity fractions indicated near-equilibrium for some OCPs (p,p'-DDE, chlordanes, trans-nonachlor and dieldrin) and net volatilisation for others (p,p'-DDT, o,p'-DDT, toxaphene, gamma-HCH). Chiral analysis showed that enantioselective degradation of (+) or (-) o,p'-DDT in soil was accompanied by enrichment or depletion of the corresponding enantiomers in the overlying air, although there appeared to be some dilution by racemic o,p'-DDT from regional air transport.
authors.affiliation: Centre for Atmospheric Research Experiments (CARE), Meteorological Service of Canada, 6248 Eighth Line, Egbert, Ontario, Canada L0L 1N0. terry.bidleman@ec.gc.ca
authors.forename: Terry F
authors.initials: TF
authors.lastname: Bidleman
authors.forename: Andi D
authors.initials: AD
authors.lastname: Leone
mesh_terms: D000383:Agriculture; D000393:Air Pollutants / Q000032:analysis; D000407:Alabama; D004784:Environmental Monitoring / Q000379:methods*; D004787:Environmental Pollution / Q000032:analysis*; D006843:Hydrocarbons, Chlorinated; D007306:Insecticides / Q000032:analysis*; D008145:Louisiana; D010573:Pesticide Residues / Q000032:analysis; D012989:Soil Pollutants / Q000032:analysis; D013781:Texas
chemical_list: D000393:Air Pollutants; D006843:Hydrocarbons, Chlorinated; D007306:Insecticides; D010573:Pesticide Residues; D012989:Soil Pollutants