Organochlorine pesticides in residential soils and sediments within two main agricultural areas of northwest Mexico: Concentrations, enantiomer compositions and potential sources

The agricultural Mexicali and Yaqui valleys (MV, YV) in northwest Mexico were heavily treated with organochlorine pesticides in the past. Residential soils and agricultural drain sediments were sampled in 2008-2009 and analyzed for DDTs (o,p'-and p,p'-isomers of DDE, DDD and DDT); hexachlorocyclohexanes (alpha-, beta-, gamma- and delta-HCH) and chlordanes (trans-chlordane, cis-chlordane, heptachlor and heptachlor exo-epoxide). Geometric means (GMs) (ng g(-1) dry weight) were: MV soils (n = 27) EDDT 22, EHCH 0.80, ECHL 0.88; YV soils (n = 25) Sigma DDT 5.0, Sigma HCH 0.23, ECHL 0.67; MV sediments (n = 3) EDDT 5.0, IFICH 0.23, ECHL 0.53; YV sediments (n = 8) Sigma DDT 2.6, Sigma HCH 0.12, Sigma CHL 0.090. GMs were significantly higher (p < 0.05) in MV than YV soils for Sigma DDT and Sigma HCH, but not for Sigma CHL. Comparison to worldwide regulatory guideline values (RGVs) for residential soils showed all compounds below mean or GM RGVs, but above the lowest RGV in some cases. Low p,p'-DDT/(p,p'-DDT + p,p'-DDE) in most soils indicated aged residues. Lack of p,p'-DDT metabolism might account for its dominance in a few soils. HCH isomer profiles suggested aged technical HCH in the YV, and technical HCH + lindane in the MV. Heptachlor dominated the ECHL, probably from application of technical heptachlor as well as chlordane. Chiral compounds were nonracemic in soils and sediments and indicated enantioselective microbial degradation of (+)alpha-HCH, (-)trans-chlordane, (-)cis-chlordane and (+)o,p'-DDT. Depletion of (+)o,p'-DDT in soils may account for similar enantiomer signatures previously reported in air of northwest Mexico. (C) 2017 Elsevier Ltd. All rights reserved.