Spatial-temporal distribution characteristics of DDTs in oysters (Crassotrea rivularis) along Guangdong coast,China

In each spring during 1989—1993 and 2003—2012,oyster samples(Crassotrea rivularis Gould)were collected from 16 sites along Guangdong coast,China.The contents of DDTs(including o,p'-DDT,p,p'-DDT,p,p'-DDD,p,p'-DDE)were detected by gas chromatography with electron capture detector.Based upon the detected data of DDTs in oysters along Guangdong coast and the data taken from the pollution investigations of Guangdong coastal zone,China during 1980—1985,the residues levels,spatial and temporal trends and compositions of DDTs in oysters were analyzed and discussed.Also,food safety and biological quality of DDTs in oysters were assessed.The results indicated that DDTs was detected in 95.9% of the samples,and in the detectable samples,DDTs contents ranged from 0.11 to 76.3 ng/g with an average of 3.87 ng/g on wet weight basis.DDTs contents decreased obviously during the early period after DDTs was banned from 1980s to early 1990s,but presented a gentle increase owing to possible inputs of new DDTs in 2003—2007,and with the national implementation measures for the Stockholm Convention,DDTs contents maintained steady finally between in 2008—2012.In early 1980s,DDTs contents in Pearl River Estuary were much higher than East Guangdong coast and West Guangdong coast,but the difference of DDTs contents from these three coasts narrowed gradually with time and became not significant statistically since 1989(P0.05).The composition analysis of DDTs in the oyster samples showed that DDTs residues were sourced mainly from the historical usage,but the higher ratios of DDT/(DDD+DDE)and o,p'-DDT/p,p'-DDT(1)indicated that there was probably new input of DDTs which might come from dicofol in periods of 1989—1993 and 2003—2007.The DDTs residues levels of all oyster samples were below the national residual limit standards,during the period of 1980s—1990s and 2003—2007,there was only 4.6% of oyster samples exceeded US EPA reference limits(14.4 ng/g),and 6.7% of samples exceeded the requirement of the first grade of the National Marine Biological Quality Standard of China(10 ng/g).The biological quality of DDTs in oysters was good and the food safety has been acceptable in recent years.