The sampler was rinsed with river water at the site prior to 

 sediment collection. The sample was placed in prewashed (Biosoap wash, 

 ultrapure water rinse) high density polyethylene containers. High 

 density polyethylene containers are relatively inert and are optimal for 

 samples contaminated with a variety of chemicals (ASTM 1991). The con- 

 tainers were filled completely to achieve zero sample head space. 

 Sample containers were placed on ice as soon as possible following 

 collection (never exceeding 2 hours). Samples were transported to the 

 laboratory and stored at 4°C for no more than two weeks as recommended 

 by Anderson et al . (1984). 



We used sediment porewater in our toxicity tests. Numerous stud- 

 ies (Adams et al . 1985; Swartz et al . 1985; Knezovich and Harrison 1988; 

 Connell et al . 1988; Swartz et al . 1988, Di Toro et al 1992) have shown 

 that porewater is an appropriate surrogate for bulk sediment. Porewater 

 can be collected from sediment samples by several methods: 

 centrifugation, squeezing, suction, and equilibrium dialysis (ASTM 

 1991). Centrifugation is generally used if large volumes of porewater 

 are required (Edmunds and Bath 1976). Constituents such as salinity, 

 dissolved inorganic carbon, ammonia, sulfide, and sulfate are generally 

 not affected as long as oxidation is prevented; however, dissolved 

 organic carbon (DOC) and dimethyl sufide may be significantly reduced 

 using this method (Howes et al . 1985). Sediment porewater was extracted 

 by centrifugation at 4000 g (g = the acceleration due to gravity) at 4°C 

 for 45 minutes. Sample porewater was stored with zero head space at 4°C 

 in a decontaminated cubitainer for a maximum of 1 week. The time from 

 collection to testing ranged from 1 to 6 days, and averaged 2.6 days for 



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