Chlorinated organic pollutants in global flooded soil and sediments: Pollution status and potential risk

Residual effects of chlorinated organic pollutants on microbial community and natural redox processes in coastal wetlands

Chlorinated organic pollutants (COPs) are common in flooded environments. To examine the residual status and effects of COPs on flooded environments, a survey of 7 coastal wetlands in Zhejiang, East China was conducted. Total COP concentrations detected from 95.69 to 412.76 ng g-1 dw. Gamma-HCH and o,p'-DDT posed the greatest risk with exceedance rates of 100% according to sediment quality guidelines. Samples with higher COP pollution had higher microbial diversity, more complex microbial networks, more deterministic community assembly processes and lower microbiome stability, indicating an improved soil function for balance cycle of substances, especially for COP degradation. Further analysis using quantitative real-time PCR suggested COP-dechlorination interacted with natural redox processes, especially sulfate reduction and methanogenesis. The positive correlation between CH4 and pentachlorobenzene indicated a potential increase in greenhouse gas emissions caused by COP pollution. Correlation between dsr gene and COPs demonstrated the ability of sulfate-reducing bacteria to degrade COPs. Particularly, facultative OHRB such as sulfate-reducing bacteria hold significant importance in the process of COP-dechlorination. This finding provides a reference for COP pollution remediation. Collectively, our study offers new insight into the residual effect of COPs in coastal wetlands and contributes to an improved understanding of bioremediation strategies for COP pollution.

Solar-assisted oxidation of organochlorine pesticides in groundwater using persulfate and ferrioxalate

The oxidation of hexachlorocyclohexane isomers in the aqueous phase (Milli-Q and groundwater) was studied using persulfate activated by ferrioxalate and solar light at circumneutral pH. The experiments were conducted in a solar simulator reactor with local radiation fluxes qw= 1.12·10-7 E cm-2s-1 and in compound parabolic collectors with solar light (qw≈10-7 E cm-2s-1) for 390 min. The effect of activator dosage (18-125 μM ferrioxalate) and persulfate concentration (520-2600 μM) on hexachlorocyclohexane conversion and oxalate and oxidant consumption was analyzed. Conversion of about 95% of β isomer was achieved at 390 min using 1300 μM of initial persulfate and 63 μM of Fe3+ concentration despite this β isomer being the most recalcitrant to oxidation (XHexachlorocyclohexanes=0.98). Dechlorination above 80% was achieved under these conditions, analyzing the chlorides released into the water. The influence of chloride and bicarbonate on hexachlorocyclohexanes degradation was analyzed in milli-Q water and in groundwater. Hexachlorocyclohexane conversion at 390 min decreases from 98% to 83, 75 and 65% in the presence of chloride, bicarbonate or groundwater, respectively. Results obtained with compound parabolic collectors and solar light using 2600 μM Na2S2O8 and 63 μM Fe for removing hexachlorocyclohexanes agreed with those from the solar simulator reactor, supporting using solar light to activate persulfate for sustainable abatement of persistent organic pollutants in aqueous matrixes.