What's causing toxicity in sediments? Results of 20 years of toxicity identification and evaluations.

Sediment toxicity identification and evaluation (TIE) methods have been used for 20 yr to identify the causes of toxicity in sediments around the world. In the present study, the authors summarize and categorize results of 36 peer-reviewed TIE studies (67 sediments) into nonionic organic, cationic, ammonia, and "other" toxicant groups. Results are then further categorized according to whether the study was performed in freshwater or marine sediments and whether the study was performed using whole-sediment or interstitial-water TIE methods. When all studies were grouped, nonionic organic toxicants, either singly or in combination with other toxicants, were implicated in 70% of all studies. When studies were divided into interstitial-water TIE methodology compared with whole-sediment TIE methodology, results indicated that studies performed using interstitial-water TIE methods reported nonionic organic toxicity slightly more often than toxicity from cationic metals (67% compared with 49%). In contrast, studies using whole-sediment TIE methods report nonionic organic chemical toxicity, either singly or in combination with another toxicant, in 90% of all sediments tested. Cationic metals play a much smaller role in whole-sediment TIE studies-fewer than 20% of all sediments had a metals signal. The discrepancy between the 2 methods can be attributed to exposure differences. Contrary to earlier findings, ammonia generally plays only a minor role in sediment toxicity.