In situ remediation of obsolete chlorinated pesticides using a combination of immobilization and bioremediation

Chlorinated obsolete pesticides pose a risk to health and the environment due to their persistence. Low-cost strategies such as bioremediation have been successfully demonstrated in laboratory and microcosm studies at low pesticide concentrations. Few studies have explored in situ bioremediation under field and uncontrolled conditions. A field trial was conducted utilizing a combination of biostimulation and immobilization, to remediate a contaminated soil with above threshold levels of Endrin and Dieldrin. The soil was treated with biochar, manure and a bioinnoculant created from incubation of native soil. Biochar and manure were incorporated into the soil to a depth of 20 cm and the bioinoculant applied on the surface. A stratified systematic sampling design was used to collect soil at 2-month intervals up to 10 months after incubation (MAI) from 9 zones at 0–20 and 20–40 cm. Vegetation samples were collected using a 1 m quadrat in each zone. Soil and vegetation samples were analysed for Endrin, Endrin Ketone and Dieldrin. Average concentrations of all pesticides decreased from baseline up to 6 MAI in the 0–20 cm layer, followed by an increase and decrease at 8 and 10 MAI, respectively. At 6 MAI pesticides levels were below soil screening levels (SSL) at both depths, except for Endrin Ketone. At the end of the trial, Endrin and Endrin Ketone concentration were below SSL, however, Dieldrin concentration was above. Pesticide concentrations in plant tissue followed a similar decreasing pattern with time but remained near undetectable from 6 MAI. The treatment combination showed potential for reducing pesticide concentrations in soil and vegetation.