The comminution of large quantities of wet sediment for analysis and testing with application to dioxin-contaminated sediments from lake Ontario

When preparing field samples for analysis and testing, it is invariably necessary to split the sample into representative subsamples. If the mass of the original sample is of the order of 1 000 kg (dry-mass basis), then subsamples that are about 100 000-1 000 000 000 times smaller are required for chemical analysis. With such large reductions in size, the representability of the subsample is a concern. Here, a systematic method for preparing representative subsamples from large quantities of wet sediment is described. The sediment is passed through a commercially available slurry sampler that provides 1/20 ^th splits. Further splits are obtained with a custom-built churn splitter. The procedure was applied to sediments collected from Lake Ontario, USA, and from the lower Fox River and Green Bay, Wisconsin, USA. Its efficacy was evaluated by dioxin and total-organic-carbon analy-sis for the sediments from Lake Ontario and by analysis of the ammonia contained in the pore-water of the sediments from the Fox River and Green Bay.