Mercury in Waters of the Derwent Estuary—Sample treatment and analysis

A reliable procedure for mercury sample collection, storage and analysis has been established for estuarine waters using relatively inexpensive reagents and apparatus. SnCl2-reactive (easily reducible), acid-labile (30-day storage of unfiltered samples with 1% HNO3), and particulate mercury were determined in water samples from the Derwent Estuary using a preconcentration step followed by syringe-injection cold-vapour atomic absorption spectroscopy. Acid-labile and particulate mercury results were closely correlated, indicating that suspended particulate matter was the main contributor to mercury in the water column. Bottom waters in mid-reaches of the estuary displayed the highest acid-labile mercury concentrations, with values up to 350 ng l−1 consistently exceeding national guidelines (100 ng l−1), but indicating improvement over values of 16 000 ng l−1 reported in 1975. Further experiments confirmed the high mercury scavenging ability of suspended particulate matter in the Derwent Estuary, and indicate the ultimate fate of these particles is the dominant sink for inorganic mercury in the estuary.