Study On Biodegradation Characteristics Of Organochlorine Pesticides In Sediment Of Haihe River

Organochlorine Pesticides (OCPs) as one class of important chlorinated organic compounds are widely used in industrial and agricultural production, but their residues in the environment and deleterious effect are also unnegligible. Studies showed that biodegradation is the main way to remove these pollutants from the environment. Most studies are about the degradation of OCPs under intensified conditions. Natural environment has the ability of self-repairing. Natural degradation is a ubiquitous process in the polluted environment. Study on this aspect is helpful to understand the fate of OCPs and increase the background knowledge of in-situ remediation.This paper selected hexachlorocyclohexane (HCHs:α-HCH,β-HCH,γ-HCH andδ-HCH) and dichlorodiphenyltrichloroethane (DDTs: o,p'-DDT and p,p'-DDT) as object compounds and collected superficial sediments in main stream section of Haihe River in Tianjin as experiment materials to investigate the effects of dissolved oxygen (DO) and temperature on OCPs biodegradation in the sediments, and the results were also compared with OCPs biodegradation in the water-sediment interface. The results obtained in this work are as follows:(1) The process of OCPs biodegradation in both sediments and the water-sediment interface followed a first-order kinetic. The biodegradation rate constant k of HCHs was 0.0111⁰.0619d-1 forα-HCH, 0.0102⁰.0339d-1 forβ-HCH, 0.0198⁰.0858d-1 forγ-HCH, and 0.0120⁰.0586d-1 forδ-HCH, respectively. The biodegradation rate constant k of DDTs was 0.0253⁰.0474d-1 for o,p'-DDT, 0 .0247⁰.0505d-1 for p,p'-DDT.δ-HCH and o,p'-DDT had a lag time during the process of degradation. Comparing with studies reported, organochlorine pesticides had stronger biodegradation ability in sediments of Haihe River.(2) At 25℃, the k values of OCPs under aerobic and anaerobic conditions in superficial sediments of Haihe River were in the order of k_γ-HCH >k_α-HCH >k_δ-HCH >k_β-HCH;k_o,p'-DDT >k_p,p'-DDT. At 25℃, the k of OCPs in the water-sediment interface was k_γ-HCH > k_δ-HCH >k_β-HCH >k_α-HCH, k_o,p'-DDT >k_p,p'-DDT under anaerobic condition, and k_γ-HCH >k_δ-HCH >k_α-HCH >k_β-HCH, k_o,p'-DDT >k_p,p'-DDT under aerobic condition, respectively. At 15℃, the k of OCPs in superficial sediments of Haihe River was k_β-HCH >k_γ-HCH >k_δ-HCH >k_α-HCH, k_o,p'-DDT >k_p,p'-DDT under aerobic condition, and k_β-HCH >k_α-HCH >k_γ-HCH >k_δ-HCH, k_p,p'-DDT >k_o,p'-DDT under anaerobic condition. The results exhibited that biodegradation rate under aerobic condition was significantly different with that under anaerobic condition.(3) Effect of temperature on OCPs biodegradation in the sediments of Haihe River. The degradation rates ofα-HCH,γ-HCH andδ-HCH under aerobic condition at 25℃were higher than those at 15℃. The degradation rates ofα-HCH,γ-HCH andδ-HCH under anaerobic condition at 25℃were higher than those at 15℃. The biodegradation rates of o,p'-DDT and p,p'-DDT were lower than those under anaerobic condition at 15℃. The biodegradation rates ofα-HCH,γ-HCH andδ-HCH increased with the temperature, but the others not.(4) Under anaerobic condition at 25℃, the biodegradation rates of OCPs in the water-sediment interface were lager than those in the superficial sediment, while under aerobic condition, the biodegradation rates ofα-HCH,γ-HCH andδ-HCH in the superficial sediment were lager than those in the water-sediment interface. But the biodegradation rates of o,p'-DDT and p,p'-DDT were lower than those in the water-sediment interface. The biodegradation rates of organochlorine pesticides changed significantly in different media.