Spatiotemporal evaluation of organochlorine pesticide residues in bottom sediments of the Rio de Ondas hydrographic basin, western Bahia, Brazil

The Rio de Ondas Hydrographic Basin (ROHB), Bahia state, Brazil, is located in a region with abundant water resources and is highly impacted by intense agricultural activity. In such a scenario, the use of organochlorine pesticides can represent a potential risk to the aquatic environments, due to their persistence, high bioaccumulation capacity, and high toxicity. Thus, organochlorine pesticide residues in bottom sediment samples from rivers on eighteen sites distributed along the ROHB in the dry and rainy periods were analyzed by gas chromatography coupled with mass spectrometry. The validated method showed no matrix effect, recoveries ranging from 82% (β-HCB) to 118% (DDD), limits of detection between 0.003 ng g −1 (α-HCH) and 0.011 ng g −1 (DDT), limits of quantification of 0.010 ng g −1 (α-HCH) to 0.036 ng g −1 (DDT), repeatability with the highest relative standard deviation of 0.97% (α-hexachlorocyclohexane at 2.000 ng g −1 ), and inter-day precision ranging from 10% (aldrin at 0.050 ng g −1 and 0.600 ng g −1 and α-endosulfan at 0.600 ng g −1 ) to 25% (β-endosulfan at 0.050 ng g −1 ). Although most compounds were banned since 1985, it was observed that their residues were widely distributed in the ROHB, with the total concentrations varying from 3.242 ng g −1 (P02) to 12.052 ng g −1 (P17) and from 0.313 ng g −1 (P14) to 30.861 ng g −1 (P13) in the dry and rainy periods, respectively, which may be related to historical contamination and/or prohibited use. Moreover, the spatiotemporal variation showed the highest concentrations of organochlorine pesticide residues in the rainy season, coinciding with the planting period.