Toxicity and biodegradability evaluation of HCHs-polluted soils after persulfate remediation treatments

Abstract

Soils contaminated with lindane (γ-hexachlorocyclohexane, γ–HCH) wastes are widespread due to its massive production and high persistence. A noticeable case is in the Sardas and Bailín landfills (Spain), where INQUINOSA discharged tons of lindane wastes. The current work evaluates the remediation of polluted surface soil (HCHs = 409 mg kg−1) from these emplacements by two persulfate (PS)-activated on-site treatments: thermal (PS/T) and alkaline activation, the last one also intensified by temperature (PS/NaOH/T). The possible adverse effects of the chemical treatments on acute toxicity (associated with reagents, pH, by-product generation, etc.) of all phases involved (soils, soil organic extracts, reaction supernatants, and soil elutriates) towards Vibrio fischeri and Artemia salina were evaluated. Biodegradability assays were also performed. Both treatments presented high efficiency in pollutant degradation (XHCHs ≥ 90 % and dechlorination degree ≈ 80 %). After PS/T treatment, the soil and organic extract acute toxicity (Vibrio fischeri and Artemia salina) was reduced to the minimum level, and neither the reaction supernatant nor the soil leachate exhibited acute toxicity. Vibrio fischeri-soil acute toxicity remained unaltered after PS/NaOH/T treatment, which was attributed to the high NaOH concentration used. The toxicity of this soil elutriate was low, although that of aqueous reaction supernatant presented non-negligible values. In the case of Artemia salina bioassay, the alkaline treatment leads to a more significant decrease in toxicity than the thermal activation of PS. Finally, the biodegradability of treated soils increased, highlighting the suitability of PS-activated treatments for the remediation of HCHs-polluted soils.