Hexabromocyclododecanes In Surface Sediments From Shanghai, China: Pollution Characterization, Spatial Distribution And Seasonal Variation

As a kind of persistent organic pollutants (POPs), hexabromocyclododecanes(HBCDs) has been of great concern due to its persistency, bioaccumulation, toxicityand potential for long range environmental transport. Shanghai is the center forindustrial and economic development in China. With the increasing of industries ofbuilding materials, textile, electronic information products, automobile, petrochemicaland fine chemical and population, the pollution of flame retardants in the environmenthave been aggravating. Available studies have shown that POPs are ubiquitousenvironmental contaminants in Shanghai. However, little information was availableon HBCDs in environment mediums from Shanghai, especially in sediments.The levels, possible sources, spatial distribution, diastereoisomer-specificprofiles and seasonal variation of HBCDs in surface sediments from Shanghai weresystematically investigated for the first time. Moreover, the correlations between theconcentrations of individual diastereoisomers and the total of HBCDs (designed asΣHBCD) and total organic carbon (TOC) were analyzed and the mass inventories ofHBCDs in surface sediments of Shanghai were estimated. The study aimed tounderstanding the contamination status of HBCDs in sediments of Shanghai and toproviding the scientific basis for making a reasonable control scheme of HBCDs. Inaddition, the present study is of both theoretical and practical significance to assessecotoxicological effects of HBCDs and protect human and environment from harmfuleffects of HBCDs. The major findings and conclusions are as follows:(1) HBCDs was detected in all surface sediment samples collected fromShanghai, indicating that HBCDs has become ubiquitous environmental contaminantsin this region. The levels of ΣHBCD in surface sediment samples from the HuangpuRiver, the Suzhou Creek and the Yunzao Creek ranged from0.05to6.87ng g-1on adry weight basis (dw), with a mean value of1.61ng/g dw. In general, our studypresented a relatively low HBCDs level compared to levels measured in domestic andother parts of the world. In addition, the concentrations of ΣHBCD in surface sediment samples from the other rivers in Shanghai ranged from0.015to13.7ng g-1dw, with a mean value of3.23ng/g dw. The mean concentrations of ΣHBCD followedthe order of the chemical/textile industrialized areas (4.97ng/g dw) the otherSampling areas (2.44ng/g dw) the Huangpu River, the Suzhou Creek and theYunzao Creek (Samples collected in the Summer,2.02ng/g dw).(2) The profile of HBCD diastereoisomers in sediment samples from theHuangpu River, the Suzhou Creek and the Yunzao Creek was41.1%α-HBCD,10.8%β-HBCD, and48.1%γ-HBCD, and from the other rivers in Shanghai was39.6%α-HBCD,9.9%β-HBCD, and50.5%γ-HBCD, which are both not consistent withthose of commercial formulations. This may be due to thermal isomerization fromγ-HBCD to α-HBCD at temperatures above160°C during industrial application of theflame retardant and slower degradation rate of α-HBCD compared to γ-HBCD inanaerobic conditions.(3) Spearman correlation analysis showed that all three diastereoisomers weresignificantly and positively correlated with each other and with ΣHBCD, indicatingthat they share similar sources in our study areas. However, no significant correlationwas found between TOC and concentration of ΣHBCD in surface sediments fromShanghai, suggesting that the spatial distribution of HBCDs was not constrained bythe TOC content of sediments.(4) This paper first studied the seasonal variation (winter and summer) ofHBCDs concentrations in sediments from the Huangpu River, the Suzhou Creek andthe Yunzao Creek in Shanghai. The result showed that the concentrations of ΣHBCDin the summer (mean2.02ng/g dw) were significantly higher than those in the winter(mean1.20ng/g dw)(paired t test, p<0.01). The variation may be attributed to acombined effect of several factors, such as temperature and wet deposition.(5) This study estimated the mass inventory of ΣHBCD in surface sediments ofShanghai for the first time. The result showed that the mass inventory (averageinventory) of ΣHBCD in the surface sediments estimated to be135.9kg (21.2ng/cm2)was comparable with the average inventory of ΣHBCD in Tokyo Bay and suggestedthe great influence of human activity on rivers and lakes ecosystem.