Nanoparticle immunotoxicity using an environmental sentinel as a model

[摘要] Although there is no statutory limit for molybdenum in UK or European drinking water, the WHO since 1993 have recommended a health-based guideline value for molybdenum in drinking water of 70 ��g L�C1. This report provides an assessment of the occurrence and distribution of molybdenum in UK surface waters, groundwaters and drinking waters in order to assess the implication for the UK water industry should legislation to limit the concentrations of molybdenum in drinking water, commensurate with the WHO guideline value, be introduced in the coming years. A survey has been carried out of molybdenum (Mo) concentrations in drinking water from twelve public-supply sources distributed across England & Wales, monitored up to four times over an 18-month period, together with domestic taps from three of their supply areas. As the scale of the survey was limited, a formal probability-based survey design was not possible. Instead a purposive sampling approach was adopted, focusing on those regions where the risk of exceedence of the WHO guideline value, based on available surface-water and groundwater data, was believed to be greatest. The design adopted was therefore nonprobabilistic and not able to provide statistical estimates of probabilities of exceedence. However, it was considered appropriate for reducing uncertainty over sources of greatest risk. Public-supply sources included five groundwater sources (one a mine sough), four river sources and three upland reservoir sources. For three of the public-supply sources investigated, molybdenum concentrations for all samples were below the detection limit of 0.03 ��g L�C1. For the remaining nine sources, analysis of variance confirmed that significant differences existed in molybdenum concentration between sites but not within sites at different sampling times. Although concentrations in surface waters were generally more variable than in groundwaters, the results did not show evidence of a notable seasonal effect. All analysed concentrations were more than an order of magnitude lower than the WHO guideline value for Mo of 70 ��g L�C1. Tapwater samples were analysed from eight households in each of three areas: Bangor (Gwynedd), Mickleover (Derbyshire) and Haverhill (Suffolk). Sampling at each tap involved collection of a morning first-draw (pre-flush) sample and a post-flush sample. Analysis showed a remarkable uniformity in molybdenum concentrations at each location, the variability being very small between houses (old and new), between pre- and post-flush samples, and between the tapwater and respective source-water samples. The results suggest that water distribution pipework has a negligible effect on supplied tapwater molybdenum concentrations. All tapwater samples from Bangor had molybdenum concentrations below detection limit, consistent with those in the public-supply source water. Tapwaters from Haverhill were not significantly different from their source waters (p >0.05). Mickleover tapwaters had lower Mo concentrations than source waters. The differences were statistically significant (p 20 mg kg�C1) can be found in some argillaceous deposits, especially black shales and other sulphide-rich deposits. Relatively high molybdenum concentrations are also found in some ironstones and granites. Concentrations of molybdenum in 65,447 stream sediments from England & Wales (G-BASE data) range up to 309 mg kg�C1 but with a 90th percentile value of just 2.9 mg kg�C1. Analysis of 5874 stream-sediment samples from Northern Ireland showed concentrations ranging up to 86 mg kg�C1 but with a 90th percentile of 6.7 mg kg�C1. Concentrations of molybdenum in surface waters and groundwaters in Britain are usually very low. Analyses of 96 lakewater samples monitored in 2004 from Lake Windermere and Esthwaite Water in Cumbria have concentrations of 0.1 ��g L�C1 or less. Analyses of 11,562 streamwater samples from the G-BASE dataset have a range of <0.05�C230 ��g L�C1 although the 10�C90th percentile range is much narrower, 0.08�C2.45 ��g L�C1, with a median value of just 0.57 ��g L�C1. Analyses of water samples from the LOIS rivers also typically have median concentrations <0.1�C120 ��g L�C1 but with a 10�C90th percentile range of 0.1�C1.5 ��g L�C1 and a median of 0.12 ��g L�C1. Only three samples (0.21%) have concentrations in excess of the current WHO guideline value. Median concentrations distinguished by source type (springs, boreholes, wells, mine drainage) are all close to or less than 1 ��g L�C1, although relatively high concentrations characterise mine-drainage waters (0.60�C6.0 ��g L�C1, median 1.4 ��g L�C1). These are likely derived by the release of molybdenum following oxidation of sulphide minerals. Relatively high molybdenum concentrations appear to be a particular feature of reducing (anaerobic) groundwaters and groundwaters with prolonged residence times in host aquifers. The highest observed concentrations are found in reducing groundwaters from greensand aquifers (Lower Greensand, Carstone, Spilsby Sandstone). The ranges observed in both groundwaters and surface waters indicate that molybdenum concentrations in Britain rarely occur in excess of or approaching the WHO guideline value for molybdenum in drinking water. In the event that a new drinking-water limit at a comparable concentration (70 ��g L�C1) is introduced for molybdenum in national or European legislation in the coming years, our results suggest that molybdenum should not pose a significant problem for the UK water-supply industry.

[发布机构] NERC/Centre for Ecology & Hydrology

[效力级别] Ecology and Environment