Abstract
In recent years, contamination by dicofol-type DDTs has attracted immense concern as a new source of DDT pollution. In this study, sediment samples from a dicofol manufacturing factory in Tianjing, China exhibited serious DDT contamination [p,p'-DDE (115.27 mg kg -1 ) and p,p'-DDT (11.84 mg kg -1 )]. Results of the batch experiments showed that total DDT degradation rates increase as S2O8 2− /Fe 2+ molar ratios increase. The S2O8 2− /Fe 2+ molar ratios used in this study were as follows: 60/10 < 10/30 < 20/30 < 60/50 < 60/20 < 40/30 < 60/40 < 60/30 < 80/30. Their corresponding degradation rates were 31, 43, 52, 69, 70, 71, 72, 89, and 91 μg g -1 , respectively. The optimal S2O8 2− /Fe 2+ molar ratio was 60/30, which resulted in 64% and 96% degradation of p,p'-DDE and p,p'-DDT, respectively. However, when an excessive amount of ferrous ion was used (<S2O8 2− /Fe 2+ molar ratio of 60/30), then competition for SO4 − between ferrous ion and DDTs resulted in decreased DDT degradation efficiency and increased persulfate decomposition (represented by the generated amount of sulfate). Our results implied that a slow and steady production of sulfate free radicals is favorable for DDT degradation, and that Fe 2+ availability plays an important role in controlling persulfate reactions activated by ferrous ion. Fe 2+ -activated persulfate oxidation may be significant in developing environment friendly and fast-remediation options for DDT-contaminated sediments and soil. Therefore, this study contributes to current knowledge on remediating DDT contamination.
Highlights
DDT [1,1,1-trichoro-2,2-bis(p-chlorophenyl)-ethane] is one of the persistent organic pollutants (POPs) identified by the Stockholm Convention on POPs which has been extensively used for controlling agricultural pests and disease-carrying insects such as malaria vectors (Zitko, 2003; Kamanavalli & Ninnekar, 2004)
Our results implied that a slow and steady production of sulfate free radicals is favorable for DDT degradation, and that Fe2+ availability plays an important role in controlling persulfate reactions activated by ferrous ion
DDT degradation and persulfate decomposition were observed by calculating the amount of ferrous ion and persulfate at ambient temperature (20 °C)
Summary
DDT [1,1,1-trichoro-2,2-bis(p-chlorophenyl)-ethane] is one of the persistent organic pollutants (POPs) identified by the Stockholm Convention on POPs which has been extensively used for controlling agricultural pests and disease-carrying insects such as malaria vectors (Zitko, 2003; Kamanavalli & Ninnekar, 2004). The manufacture and application of DDTs have been restricted since the 1970s because of their negative effects, traces of DDTs can still be detected in air, water, soil, sediments, and organisms (Bettinetti et al, 2008; Yao et al, 2006). DDE has been reported to be more persistent than DDT and can be detected in soil decades after the application of DDT (Thomas et al, 2008). As a potent androgen antagonist (Kelce et al, 1995), DDE has been found to be the most abundant DDT component in sediments (Eganhouse & Pontolillo, 2008), fish, and humans (Kamanavalli & Ninnekar, 2004)
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