Development of an electrolysis system for tritium enrichment in superficial water samples.
Tritium present in the environment gradually decreased in the last decades and nowadays it has reached extremely low activity concentrations. The purpose of the present work is the implementation of a tritium enrichment system in water samples using electrolytic techniques and pure nickel and iron electrodes. In the present work a mean tritium enrichment factor of 13.0 +/- 3.2 was obtained. This result should allow to reach a minimum detectable activity of tritium in water samples of about 1 tritium unit (TU) or less. The present enrichment system necessitates further adjustments and improvements, such as a cooling system in order to reduce the tritium losses due to evaporation.
A compact tritium enrichment unit for large sample volumes with automated re-filling and higher enrichment factor.
Tritium (3H) in natural waters is a powerful tracer of hydrological processes, but its low concentrations require electrolytic enrichment before precise measurements can be made with a liquid scintillation counter. Here, we describe a newly developed, compact tritium enrichment unit which can be used to enrich up to 2L of a water sample. This allows a high enrichment factor (>100) for measuring low 3H contents of <0.05TU. The TEU uses a small cell (250mL) with automated re-filling and a CO2 bubbling technique to neutralize the high alkalinity of enriched samples. The enriched residual sample is retrieved from the cell under vacuum by cryogenic distillation at -20°C and the tritium enrichment factor for each sample is accurately determined by measuring pre- and post- enrichment 2H concentrations with laser spectrometry.
Human exposure to methylmercury from crayfish (Procambarus clarkii) in China
Methylmercury (MeHg) accumulation in aquatic food raises global concerns about human exposure to MeHg. Crayfish is the world’s third largest farmed crustacean species and a favorite aquatic food in many countries. However, human health hazard due to MeHg exposure via crayfish consumption is unclear, partly because appropriate survey data are lacking. We report on mercury concentrations and speciation in edible tail muscle of crayfish collected from restaurants in 23 Chinese cities. On average, MeHg constituted 99.1 % of mercury in tail muscle, and MeHg concentrations were comparable with those reported for fish in China. Variation in MeHg concentrations was not attributable to broad geographic region (i.e., provinces) or tail length. For different populations, potential health risk (characterized by hazard quotient or HQ) of MeHg exposure through crayfish consumption depended largely on crayfish consumption rates. In particular, a health hazard (HQ > 1) was found for high-rate consumers (i.e., 95 %ile or higher) in some cities in the middle and lower reaches of the Yangtze River (MLYR), during the peak consumption season. Our results suggest that more attention should be paid to dietary MeHg intake via crayfish consumption in China, particularly for communities with high consumption in MLYR.