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Speciation studies are necessary to understand the biogeochemical cycling of arsenic in aquatic systems. The species of arsenic present, their behaviour and toxicity will change depending on the biotic and abiotic conditions in the water. In groundwater, arsenic is predominantly present as arsenite (As III ) and arsenate (As V ). The major arsenic species in freshwater are As III and As V and minor amounts of MMA , DMA and methylated As III have also be detected. In seawater, the arsenic speciation differs in the surface and deep zone. In addition to the above species, uncharacterized arsenic species may constitute a significant portion of the total arsenic present in some water and the identification of these compounds is necessary to fully understand the arsenic biogeochemistry in water.A knowledge of the speciation of As in natural water is important because the bioavailability and the physiological and toxicologial effects of As depend on its chemical forms. Arsenic occurs in a variety of chemical forms in water, and this is a result of many chemical and biological transformations in the aquatic environment. The mechanism of transport and biological availability of arsenic depends on the chemical species present.The main arsenic compounds detected in natural waters are arsenite [As 111 ],

The bacterial transformation of pyrene in an estuary environment, Kitimat Arm, British Columbia, Canada, was studied. A metabolite was separated from marine sediment and pore water samples and was identified as cis-4,5-dihydroxy-4,5-dihydropyrene, based on a comparison of the metabolite with the authentic standard, by using both high-performance liquid chromatography and capillary gas chromatography with mass spectrometry detection. The presence of this key metabolite of dioxygenase-mediated transformation of pyrene, along with previous pyrene degradation studies using cultures isolated from the same sediment samples, suggests a possible in situ bacterial transformation of pyrene in the Kitimat Arm environment.

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