Geochemistry and bioavailability of metals in sediments from northern San Francisco Bay

In this study, metals (Be, Cr, Mn, Fe, Ni, Cu, Zn, Ag, Cd, Pb and Hg) in the fine-grained fraction (<63 microm) from 12 sites at different locations in northern San Francisco Bay over a year period from March 2000 to March 2001 were analyzed after acid extraction. The results showed that metal concentrations in the sediments varied from site to site, whereas some of them were found elevated with respect to the sediment of Tomales Bay, CA, which has little contamination history, indicating an enrichment of the metals in the sediment samples analyzed. Sediment toxicity and bioaccumulation evaluation by a clam species, Macoma nasuta, exposed to the sediment samples collected from the six sampling sites was carried out. The results showed that the sediment samples tested significantly reduced clam survival. Toxicity of the sediments to the clam was, in part, related to elevated metal concentrations in the sediments. In order to examine geochemistry of the metals and to understand potential correlations between metal concentrations and geochemical matrix elements of the sediments, bioavailability and toxicity of the metals, detailed analysis of metal concentrations associated with total organic carbon and the Fe-oxy-hydroxides in the sediment samples was performed. The analysis showed that sediment geochemistry appeared to influence metal bioavailability and may have important impacts on the toxicity of these metals to the clam.     

Identifying optimal agricultural countermeasure strategies for a hypothetical contamination scenario using the strategy model

A spatially implemented model designed to assist the identification of optimal countermeasure strategies for radioactively contaminated regions is described. Collective and individual ingestion doses for people within the affected area are estimated together with collective exported ingestion dose. A range of countermeasures are incorporated within the model, and environmental restrictions have been included as appropriate. The model evaluates the effectiveness of a given combination of countermeasures through a cost function which balances the benefit obtained through the reduction in dose with the cost of implementation. The optimal countermeasure strategy is the combination of individual countermeasures (and when and where they are implemented) which gives the lowest value of the cost function. The model outputs should not be considered as definitive solutions, rather as interactive inputs to the decision making process. As a demonstration the model has been applied to a hypothetical scenario in Cumbria (UK). This scenario considered a published nuclear power plant accident scenario with a total deposition of 1.7x10(14), 1.2x10(13), 2.8x10(10) and 5.3x10(9)Bq for Cs-137, Sr-90, Pu-239/240 and Am-241, respectively. The model predicts that if no remediation measures were implemented the resulting collective dose would be approximately 36 000 person-Sv (predominantly from 137Cs) over a 10-year period post-deposition. The optimal countermeasure strategy is predicted to avert approximately 33 000 person-Sv at a cost of approximately 160 million pounds. The optimal strategy comprises a mixture of ploughing, AFCF (ammonium-ferric hexacyano-ferrate) administration, potassium fertiliser application, clean feeding of livestock and food restrictions. The model recommends specific areas within the contaminated area and time periods where these measures should be implemented.     

Triclosan in waste and surface waters from the upper Detroit River by liquid chromatography-electrospray-tandem quadrupole mass spectrometry

Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) is an antimicroibial disinfectant agent used in a wide array of consumer products. An analytical method based on solid-phase extraction (SPE) followed by reverse phase, liquid chromatography coupled with electrospray ionization (negative)-tandem quadrupole mass spectrometry (LC-ESI(-)-MS/MS; in the multiple reaction monitoring (MRM) mode) was developed, optimized and validated for the determination of triclosan in wastewater/sewage treatment plant (WSTP) effluent and surface waters from the upper Detroit River (Canada). The mean recoveries (+/-%RSD) of triclosan and the internal standard 2'-HO-tribromodiphenyl ether (2'-HO-BDE-28) spiked to surface water and WSTP effluent samples ranged similarly from 104+/-8% and 91+/-10%, respectively, and method limits of quantification were in the low ppb/high ppt range. However, ESI(-) enhancement was found for both analytes due to sample matrix effects, as indicated by % process efficiencies (a measure of ESI(-) enhancement/suppression), which were in the 111-128% range. We report the first known assessment of triclosan in the Detroit River watershed of the Great Lakes, which preliminarily examined the presence and UV-treatment effects on triclosan in effluent from the major WSTP serving the City of Windsor, Ontario, Canada, and fate in surface waters of the upper Detroit River. Triclosan in WSTP effluent decreased 22% after final UV treatment to a mean concentration of 63 ng/L. Concentrations were further reduced to 4 and 8 ng/L (a >90% reduction) in surface water samples from sites downstream on the Canadian shoreline of the Detroit River, which was due to dilution. Two hydroxylated tribrominated diphenyl ethers, which are structurally similar to triclosan, were also detected in WSTP effluent and surface water samples.     

Arsenic geochemistry and health

Arsenic occurs naturally in the earth's crust and is widely distributed in the environment. Natural mineralization and activities of microorganisms enhance arsenic mobilization in the environment but human intervention has exacerbated arsenic contamination. Although arsenic is useful for industrial, agricultural, medicinal and other purposes, it exerts a toxic effect in a variety of organisms, including humans. Arsenic exposure may not only affect and disable organs of the body, especially the skin, but may also interfere with the proper functioning of the immune system. This paper, therefore, generally highlights the toxic effects of arsenic as well as its mobilization in the natural environment and possible controls. It also briefly attempts to outline the impact of arsenic on the immune system, whose alteration could lead to viral/bacterial infections.     

"Reference Biospheres" for solid radioactive waste disposal: the BIOMASS methodology

The BIOMASS Theme 1 project has developed a methodology for the logical and defensible construction of 'assessment biospheres': mathematical representations of biospheres used in the total system performance assessment of radioactive waste disposal. The BIOMASS Methodology provides a systematic approach to decision making, including decisions on how to address biosphere change. The BIOMASS Methodology was developed through consultation and collaboration with many relevant organisations, including regulators, operators and a variety of independent experts. It has been developed to be practical and to be consistent with recommendations from ICRP and IAEA on radiation protection in the context of the disposal of long-lived solid radioactive wastes. The five main steps in the methodology are described in this paper. The importance of a clear assessment context, to clarify intentions and to support a coherent biosphere assessment process within an overall repository performance assessment, is strongly emphasised. A well described assessment context is an important tool for ensuring consistency across the performance assessment as a whole. The use of interaction matrices has been found to be helpful in clarifying the interactions between different habitats within the biosphere system and the significant radionuclide transfer pathways within the biosphere system. Matrices also provide a useful means of checking for consistency.     

Modelling and experimental studies on the transfer of radionuclides to fruit

Although fruit is an important component of the diet, the extent to which it contributes to radiological exposure remains unclear, partially as a consequence of uncertainties in models and data used to assess transfer of radionuclides in the food chain. A Fruits Working Group operated as part of the IAEA BIOMASS (BIOsphere Modelling and ASSessment) programme from 1997 to 2000, with the aim of improving the robustness of the models that are used for radiological assessment. The Group completed a number of modelling and experimental activities including: (i) a review of experimental, field and modelling information on the transfer of radionuclides to fruit; (ii) discussion of recently completed or ongoing experimental studies; (iii) development of a database on the transfer of radionuclides to fruit; (iv) development of a conceptual model for fruit and (v) two model intercomparison studies and a model validation study. The Group achieved significant advances in understanding the processes involved in transfer of radionuclides to fruit. The work demonstrated that further experimental and modelling studies are required to ensure that the current generation of models can be applied to a wide range of scenarios.     

Reconstruction of historical trends of PCDD/Fs and PCBs in the Venice Lagoon, Italy

Historical trends of PCDD/Fs and PCBs from the year 1900 have been reconstructed for the Venice Lagoon area by using a fugacity-based dynamic multimedia model. A novel approach to estimate the inputs to the system was applied. Emissions to the lagoon were estimated by studying dated sediment cores taken from salt marshes located in the lagoon area. These cores have recently proven to be a suitable tool to reconstruct the temporal trends of atmospheric deposition of POPs. According to the model, concentrations of PCBs and PCDD/Fs in air and water reflect the trends of their production and usage, peaking during the 1960s. The peaks in the sediment were delayed by 5-40 years depending on the congener. Predicted concentrations are in good agreement with experimental results. The most important input parameters, identified by a sensitivity analysis, are the degradation constants, K(ow), the Henry's law constant, vapour pressure, active sediment depth, sediment resuspension, and deposition rates, and water residence time in the lagoon.     

Simultaneous biological removal of endosulfan (alpha+beta) and nitrates from drinking waters using wheat straw as substrate

Nitrate and endosulfan (alpha+beta) removal was studied in an upflow biological denitrification reactor packed with wheat straw as carbon source and support particles for microorganisms. While almost complete nitrate elimination and between 65% and 70% endosulfan (alpha+beta) elimination occurred when the temperature was higher than 20 degrees C; below that value, nitrate removal efficiency decreased to about 10%. Nitrate, dissolved organic carbon (DOC), and endosulfan (alpha+beta) removal efficiencies decreased considerably at 1500 microg/l endosulfan concentration in the batch experiments. Although a high removal efficiency was observed for endosulfan (alpha+beta) and nitrate in the biological denitrification continuous reactor, the effluent water could not be used for drinking purpose because of the unacceptable levels of endosulfan (alpha+beta), colour and dissolved organic content. During the continuous study, 23.4% of the initial weight of wheat straw was lost and 24 g was consumed per gram of nitrogen removed. The results of the continuous study showed that 21.3% of the endosulfan removal was achieved by adsorption onto the wheat straw and 68.2% of the endosulfan removal occurred by biological activity and the remaining portion was detected in the effluent water.     

Preliminary evaluation of PAH sorptive changes in soil by Soxhlet extraction

This study was conducted to evaluate the influence of sorbent modification by synthetic, chemical/thermal weathering on the sorptive behavior of polycyclic aromatic hydrocarbons (PAHs). A clean sandy-clay-loam soil was subjected to Soxhlet extraction and PAH sorptive phenomena were evaluated based on quantity and quality changes in soil organic matter (SOM) and clay minerals. Critical changes in sorption capacity were found to depend on the initial PAH concentrations. Above 7 mg/l, weathering increased the PAH in comparison to that of unmodified soil, whereas it decreased when applied below this concentration. Similarly, less PAH was desorbed from the altered soil when PAH was applied above 7 mg/l. Therefore, when PAH was applied below 7 mg/l, quantitative reduction of sorbent amount (i.e., SOM and clay minerals) by soil weathering governed PAH sorptive behavior. However, when the PAH was applied above the critical limit, qualitative modifications in the sorbents facilitated an opposite trend. Sorbent swelling, removal of competing compounds, and possible changes in surface characteristics by Soxhlet extraction, together with increased concentration gradient effects were factors that resulted in dissimilar PAH sorptive phenomena, pivoting at the critical concentration.     

Mitigating Greenhouse Gas Emissions from Rice-Wheat Cropping Systems in Asia

The rice-wheat belt comprises nearly 24–27 million ha in South and East Asia. Rice is generally grown in flooded fields whereas the ensuing wheat crop requires well-drained soil conditions. Consequently, both crops differ markedly in nature and intensity of greenhouse gas (GHG) fluxes, namely emission of (1) methane (CH₄) and (2) nitrous oxide (N_2O) as well as the sequestration of (3) carbon dioxide. Wetland rice emits large quantities of CH₄; strategies to CH₄ emissions include proper management of organic inputs, temporary (mid-season) field drainage and direct seeding. As for the wheat crop, the major GHG is N_2O that is emitted in short-term pulses after fertilization, heavy rainfall and irrigation events. However, N_2O is also emitted in larger quantities during fallow periods and during the rice crop as long as episodic irrigation or rainfall result in aerobic-anaerobic cycles. Wetland rice ensures a relatively high content of soil organic matter in the rice-wheat system as compared to permanent upland conditions. In terms of global warming potential, baseline emissions of the rice-wheat system primarily depend on the management practices during the rice crop while emissions from the wheat crop remain less sensitive to different management practices. The antagonism between CH₄ and N_2O emissions is a major impediment for devising effective mitigation strategies in rice-wheat system - measures to reduce the emission of one GHG often intensify the emission of the other GHG.