The feasibility of various techniques for the separation and quantification of sediment and sediment porewaters for total Hg and methylmercury (MMHg)scentrifugation, sediment filtration, whole core squeezing, and dialysis membrane techniques (peepers)swere investigated in estuarine sediments. The concentration and distribution of iron, manganese, MMHg, and total Hg in porewaters were compared to ascertain which method provided the best technique for the collection of large volume porewater samples. Direct filtration techniques did not provide sufficient sample volume. Our studies confirmed the need to filter in an inert atmosphere. Processing in an inert atmosphere is also required for centrifugation. Centrifugation was the most difficult method, requiring extensive operator training and much attention to detail during sample processing. Core squeezing is a viable alternative but suffers from sample size problems and potential artifacts due to oxidation during processing. While peepers have advantages, the investigations here show that they need to be completely degassed before they provide reliable Hg speciation measurements, especially as they were constructed from Teflon, which can store significant amounts of oxygen. The need to deoxygenate the peepers compromises their use as a routine separation method for Hg. On the basis of the need for large volumes and the large number of samples to be collected, we concluded that centrifugation was the most reliable method for the determination of Hg and MMHg in estuarine porewaters.

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