Assessment of persistent organic pollutants and a remediation proposal at a former pesticide plant in Salamanca, Mexico

In Salamanca, Mexico, a point source of persistent organic pollutants (POPs) has been identified in an area previously occupied by the Tekchem industrial plant, which was formerly dedicated to the production and marketing of agrochemicals. This study aimed to develop a strategy to reduce the concentration of 13 POPs found in soil. The compounds studied were: α-hexachlorocyclohexane (α-HCH), β-hexachlorocyclohexane (β-HCH), γ-hexachlorocyclohexane (γ-HCH), heptachlor, heptachlor epoxide, aldrin, dieldrin, endrin, 2,4'-dichloro diphenyl dichloroethane (2,4'DDD), 4,4'-dichlorodiphenyl dichloroethane (4,4'DDD), 4,4'-dichlorodiphenyl dichloroethylene (4,4'DDE), 2,4'-dichlorodiphenyl trichloroethane (2,4'DDT), and 4,4'-dichlorodiphenyl trichloroethane (4,4'DDT). Additionally, to support the possible source distribution of POPs, a characterization of their presence in plasma from free-ranging dogs was conducted. The analyzed plasma samples revealed average concentrations of 4,4'DDT (92.20 ng/g lipid), 4,4' DDD (124.11 ng/g lipid), and 4,4'DDE (149.64 ng/g lipid), indicating that the area occupied by Tekchem plant is a source point of DDT compounds, which are bioavailable, suggesting a possible exposure to environmental. The remediation strategy involved the use of molasses and zero-valent iron (ZVI) at three different concentrations in subsurface extracted soil (up to 30 cm deep). This soil was homogenized and characterized, initially showing a concentration of ∑POPs of 6,078.34 mg/kg; the 4,4'DDT concentration is particularly noteworthy at 4,200 mg/kg. Remediation treatment results demonstrated that the 1% ZVI (w/w) application achieved a maximum reduction of ∑POPs by 96.45%. However, statistical analysis revealed no significant differences between the treatments applied. Although differences were noted when comparing the treatments with the control group and among the individual treatments, the conclusion suggests that selecting a specific agent for reducing POPs at the study site should be guided by a comprehensive cost-benefit analysis.