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Abstract: Factors controlling the transport of geogenically-derived arsenic from a coastal acid sulfate soil into downstream sediments are identified in this study with both solid-phase associations and aqueous speciation clearly critical to the mobility and toxicity of arsenic. The data from both sequential extractions and X-ray adsorption spectroscopy indicate that arsenic in the unoxidised Holocene acid sulfate soils is essentially non-labile in the absence of prolonged oxidation, existing primarily as arsenopyrite or as an arsenopyrite-like species, likely arsenian pyrite. Anthropogenically-accelerated pedogenic processes, which have oxidised this material over time, have greatly enhanced the potential bioavailability of arsenic, with solid-phase arsenic almost solely present as As(V) associated with secondary Fe(III) minerals present. Analyses of downstream sediments reveal that a portion of the arsenic is retained as a mixed As(III)/As(V) solid-phase, though not at levels considered to be environmentally deleterious. Determination of arsenic speciation in pore waters using high performance liquid chromatography/Inductively Coupled Plasma-Mass Spectrometry shows a dominance of As(III) in upstream pore waters whilst an unidentified As species reaches comparative levels within the downstream, estuarine locations. Pore water As(V) was detected at trace concentrations only. The results demonstrate the importance of landscape processes to arsenic transport and availability within acid sulfate soil environments. [ABSTRACT FROM AUTHOR]

Arsenic is a proven carcinogen often found at high concentrations in association with gold and other heavy metals. The freshwater yabby, Cherax destructor Clark (Decapoda, Parastacidae), is a ubiquitous species native to Australia's central and eastern regions, with a growing international commercial market. However, in this region of Australia, yabby farmers often harvest organisms from old mine tailings dams with elevated environmental arsenic levels. Yabbies exposed to elevated environmental arsenic were found to accumulate and store as much as 100 μg/g arsenic in their tissues. The accumulation is proportional to the concentration of arsenic in the sediment and is high enough to be of concern for people who eat the yabbies. A comparison of arsenic levels in wild and lab-fed animals also was performed. Although there was no significant difference in the level of arsenic in the various organs of the wild animals, the animals purchased from a yabby farm showed a significantly higher arsenic concentration in their hepatopancreas (3.7 ± 0.9 μg/g) compared to other organs (0.6-1.8 μg/g). Furthermore, after a 40-d exposure to food containing 200 to 300 μg/g inorganic arsenic, arsenate (As[V])-exposed animals showed a significant increase in tissue-specific arsenic accumulation, whereas arsenite (As[III])-exposed animals showed a lower, nonsignificant increase in As uptake, primarily in the hepatopancreas. These results have important implications for yabby growers and consumers alike. [ABSTRACT FROM AUTHOR]

Ten soils varying widely in chemistry and mineralogy were used to examine the physical and chemical properties that influence As sorptionprocesses in soils. The sorption of As was measured using a batch technique with Asv and AsIII concentrations addedin background solutions of NaNO3 (0.003.3 mol L-1) and a range of pH values (2.0-85). The soils generally sorbed more Asv than AsIII at equivalent As concentrations. In general, highly oxidic soils sorbed three times more As' than soils containing small amounts of oxidic minerals. The effect of pH on As sorption varied considerably among the soils. In soils with low concentrations of oxidic minerals, increasing pH had little affect onthe amount of Asv sorbed while in highly oxidic soils, sorption of Asv decreased with increasing pH. This decrease was attributed to two interacting factors, the increasing negative surface potential on the plane of sorption and increasing amount of negatively charged Asv species present in soil solution. In contrast to Asv, sorption of AsIII increased with increasing pH. The effect of ionic strength on As sorption varied between the As species. In general, there was a pH (~3) below which Asv sorption decreased with increasing ionic strength and above which the reverse occurred. For AsIII species, increasing ionic strength had little effect on the amount of As sorbed. [ABSTRACT FROM AUTHOR]