0.10–0.60 (mean 0.33), 0.06–0.41 (mean 0.19), 0.11–0.33 (mean
0.20), and 0.10–0.24 (mean 0.19), respectively (Table 3). This indicated
that DDT in seafoods of Putuo, Dinghai, and Daishan were
mainly technical DDT. The DDT in seafoods of Shengsi may partly
dicofol products. Usually, DDT can be biodegraded under aerobic
conditions to DDE and under anaerobic conditions to DDD. The
ratio of (DDE + DDD)/DDTs can be used to evaluate if the DDT pollution
occurred recently or in the past. A ratio < 0.5 may indicate
direct input of DDT, and a ratio > 0.5 reflects past usage