Organochlorine pesticides and PCBs in air in southern Mexico: 2002-2004.

Air samples were collected in southern Mexico in 2002–2004 to determine the extent of contamination with organochlorine (OC) pesticides and polychlorinated biphenyls (PCBs). The ΣDDTs ranged from 239 to 2360 pg m−3. Other prominent OC pesticides were endosulfans, toxaphene and lindane. Pesticides detected in lower concentrations include chlordanes, dieldrin, and heptachlor. Proportions of DDT compounds suggested fresh use of DDT in some locations and a mix of fresh and aged residues at others. Ratios of trans-chlordane/cis-chlordane were consistent with fresh chlordane usage or emission of residues from former termiticide applications. The ΣPCBs was relatively low at all sites. Concentrations of OC pesticides measured with passive samplers agreed well with those measured using high-volume samplers. Air back trajectory analysis suggests a complex pattern of regional atmospheric transport

Organochlorine pesticides in soils and air of southern Mexico: Chemical profiles and potential for soil emissions.

The extent of organochlorine pesticides (OCs) contamination in southern Mexico was investigated in this study. Biweekly air samplings were carried out in two sites in the state of Chiapas (during 2002–2003), and one in each state of Veracruz and Tabasco (during 2003–2004). Corresponding to the air sampling locations, soil samples were also collected to gauge the soil–air exchange of OCs in the region. ∑DDTs in soils ranged from 0.057 to 360 ng g−1 whereas those in air ranged from 240 to 2400 pg m−3. DDT and metabolite DDE were expressed as fractional values, FDDTe = p,p′-DDT/(p,p′-DDT + p,p′-DDE) and FDDTo = p,p′-DDT/(p,p′-DDT + o,p′-DDT). FDDTe in soils ranged from 0.30 to 0.69 while those in air ranged from 0.45 to 0.84. FDDTe in air at a farm in Chiapas (0.84) was closer to that of technical DDT (0.95) which is suggestive of fresh DDT input. Enantiomer fractions (EF) of o,p′-DDT in air were racemic at all locations (0.500–0.504). However, nonracemic o,p′-DDT was seen in the soils (EFs = 0.456–0.647). Fugacities of OCs in soil (fs) and air (fa) were calculated, and the fugacity fraction, ff = fs/(fs + fa) of DDTs ranged from 0.013 to 0.97 which indicated a mix of net deposition (ff \u3c 0.5) and volatilization (ff \u3e 0.5) from soil among the sites. It is suggested that DDTs in Mexico air are due to a combination of ongoing regional usage and re-emission of old DDT residues from soils. Total toxaphene in soils ranged from 0.066 to 69 ng g−1 while levels in air ranged from 6.2 to 230 pg m−3. Chromatographic profiles of toxaphenes in both air and soil showed depletion of Parlar congeners 39 and 42. Fugacity fractions of toxaphene were within the equilibrium range or above the upper equilibrium threshold boundary. These findings suggested that soil emission of old residues is the main source of toxaphenes to the atmosphere. Results from this study provide baseline data for establishing a long-term OC monitoring program in Mexico