Evaluation of geochemical methods for discrimination of metal contamination in Antarctic marine sediments: a case study from Casey Station

Detecting anthropogenic metal contamination in regional surveys can be particularly difficult when there is a lack of pre-disturbance data, especially when trying to differentiate low to moderate levels of contamination from background values. Furthermore, comparisons with other regional studies are confounded by differing analytical methods used and variations in sediment properties such as grainsize. Several types of geochemical technique, including weak acid partial extraction, strong acid extractions and total digestion have been used. Attempts have been made to overcome the influence that grainsize has on chemical concentrations in heterogeneous environments by analysing the fines, typically the mud fraction (<63 microm), in an attempt to improve the detection of anthropogenic contamination. Here we compare a weak acid partial extraction using 1M HCl and total digestion methods for a regional survey of reference and impacted sites in Antarctica using both whole sediment (<2 mm) and mud (<63 microm) fractions. The 1M partial extraction on whole sediment (<2 mm) most closely distinguished weakly, or moderately, impacted sites from reference locations. It also identified small scale within-location spatial variation in metal contamination that the total digest did not detect. Compared with total digests or analysis of the <63 microm fraction alone, this method minimised the possibility of a Type II statistical error in the regional survey - that is, failing to identify a site as being contaminated when it has elevated metal concentrations. To allow inter-regional comparison of sediment chemistry data from elsewhere in Antarctica, and also more generally, we recommend a 1M HCl partial extraction on whole sediment (<2 mm).     

Post-depositional redistribution and gradual accumulation of 137Cs in a riparian wetland ecosystem in Sweden

After the Chernobyl accident, high activity concentrations of (137)Cs (>1 MBq m(-2)) were detected in a riparian swamp in the central-eastern part of Sweden. The objective of this study was to clarify the redistribution processes behind the accumulation of (137)Cs in the wetland. A mass balance budget of (137)Cs was calculated based on soil and sediment samples and reports in the literature. Results showed that accumulation occurred over several years. Of all the (137)Cs activity discharged between 1986 and 2002 from the upstream lake, 29% was estimated to be retained in the wetland. In 2003, measurements showed that 17 kBq m(-2) sedimented on the stream banks of the wetland. Continuing overbank sedimentation by spring flooding prolongs the time that the wetland will contain high activity concentrations of (137)Cs. Consequently, organisms living in wetlands serving as sinks for (137)Cs may become exposed over long time periods to high activity concentrations.     

DETERMINISTIC MODELS FOR PREDICTING RESIDENTIAL WATER CONSUMPTION1

ABSTRACT: Forecasts of future urban water demand traditionally have been made by the projection of historic trends in per capita consumption and population. This paper outlines the use of two deterministic models to forecast the residential component of urban water demand. The models incorporate specific representation of the activities which result in water consumption at each residence. Predictions of water use can then be made by modeling the changes expected in the number of these activities and the consumption for each such activity.     

Estimation of radiation doses from (137)Cs to frogs in a wetland ecosystem

Currently, there is no established methodology to estimate radiation doses to non-human biota. Therefore, in this study, various dose models were used to estimate radiation doses to moor frogs (Rana arvalis) in a wetland ecosystem contaminated with (137)Cs. External dose estimations were based on activity concentrations of (137)Cs in soil and water, considering changes in habitat over a life-cycle. Internal doses were calculated from the activity concentrations of (137)Cs measured in moor frogs. Depending on the dose model used, the results varied substantially. External dose rates ranged from 21 to 160 mGy/y, and internal dose rates varied between 1 and 14 mGy/y. Maximum total dose rates to frogs were below the expected safe level for terrestrial populations, but close to the suggested critical dose rate for amphibians. The results show that realistic assumptions in dose models are particularly important at high levels of contamination.