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Fishery targeted species living in estuaries face multiple anthropogenic pressures including habitat contamination. However, trace metal concentrations in aquatic organisms can be highly variable, making it difficult to interpret accumulation responses. Understanding sources for metal accumulation in these organisms and their biokinetics is important for management of local fisheries and ensuring safety and quality of consumed seafood, particularly in urbanised areas. In this study, we exposed Australian sand clams, school prawns and sand whiting to a combination of cadmium (Cd), manganese (Mn) and zinc (Zn) radioisotopes 1) dissolved in seawater, 2) adsorbed to suspended sediment particles and 3) in radiolabelled food. Sand clams were sensitive to Cd, Mn and Zn uptake and accumulation from all sources because of their filter feeding physiology. Mean Cd and Zn assimilation efficiencies (AE) were higher in clams fed benthic diatoms (51, 43, 63% for Cd, Mn and Zn, respectively) than clams fed an algal flagellate species (22, 32, 33% for Cd, Mn and Zn, respectively). Metal uptake by prawns from seawater was low, whereas assimilation from diet was high (67, 59, 64% mean AEs from Cd, Mn and Zn, respectively). Sand whiting did not accumulate metals from seawater, even after concentrations were increased. Assimilation from diet (labelled prawns) was also low for sand whiting, particularly for Cd and Zn (11, 26, 14% mean AEs from Cd, Mn and Zn, respectively). These results may help explain the persistence of sand whiting in contaminated estuaries. Suspended sediment exposures showed that prawns and fish are less likely than clams to be negatively affected by disturbance events such as floods, which can bring metals into estuaries. The findings of this study have implications for fisheries management, both for protection and remediation of important habitats, and to ensure safe standards for seafood consumption by humans., (Copyright © 2019. Published by Elsevier B.V.)

The use of live animal gamma radioisotope tracer techniques in the field of ecotoxicology allows laboratory studies to accurately monitor contaminant biokinetics in real time for an individual organism. However, methods used in published studies for aquatic organisms are rarely described in sufficient detail to allow for study replication or an assessment of the errors associated with live animal radioanalysis to be identified. We evaluate the influence of some important methodological deficiencies through an overview of the literature on live aquatic animal radiotracer techniques and through the results obtained from our radiotracer studies on four aquatic invertebrate species. The main factors discussed are animal rinsing, radioanalysis and geometry corrections. We provide examples of three main techniques in live aquatic animal radiotracer studies to improve data quality control and demonstrate why each technique is crucial in interpreting the data from such studies. The animal rinsing technique is also relevant to non-radioisotope tracer studies, especially those involving nanoparticles. We present clear guidance on how to perform each technique and explain the importance of proper reporting of the validation of each technique for individual studies. In this paper we describe methods that are often used in lab-based radioecology studies but are rarely described in great detail. We hope that this paper will act as the basis for standard operating procedures for future radioecology studies to improve study replication and data quality control., (Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Bioaccumulation of As, Cd, Cu, Pb and Zn by Macrobrachium prawns was observed to occur in the Strickland River downstream of a gold mine at Porgera, Papua New Guinea. This was despite the total metal concentrations of waters and sediments indicating no difference from reference sites within tributaries. To provide information on potential sources and bioavailability of metals to prawns, an extensive range of analyses were made on waters, suspended solids, deposited sediments and plant materials within the river system. Dissolved metal concentrations were mostly sub-micrograms per liter and no major differences existed in concentrations or speciation between sites within the Strickland River or its tributaries. Similarly, no differences were detected between sites for total or dilute acid-extractable metal concentrations in bed sediments and plant materials, which may be ingested by the prawns. However, the rivers in this region are highly turbid and the dilute acid-extractable cadmium and zinc concentrations in suspended solids were greater at sites in the Strickland River than at sites in tributaries. The results indicated that mine-derived inputs increased the proportion of these forms of metals or metalloids in the Strickland River. These less strongly bound metals and metalloids would be more bioavailable to the prawns via the dietary pathway. The results highlighted many of the difficulties in using routine monitoring data without information on metal speciation to describe metal uptake and predict potential effects when concentrations are low and similar to background. The study indicated that the monitoring of contaminant concentrations in organisms that integrate the exposure from multiple exposure routes and durations may often be more effective for detecting impacts than intermittent monitoring of contaminants in waters and sediments.

Despite being essential for animal health and fitness, Se has a relatively narrow range between deficiency and toxicity, and excess Se can cause a variety of adverse effects in aquatic organisms. Amphibians are particularly vulnerable to contaminants during larval aquatic life stage, because they can accumulate toxic ions through various routes including skin, gills, lungs and digestive tract. Few attempts have been made to understand the tissue-specific accumulation of trace elements, including the impacts of chemical speciation in developing amphibian larvae. We used radiolabelled 75 Se to explore the biokinetics and tissue distributions of the two dominant forms occurring in surface waters, selenite (SeIV) and selenate (SeVI). Tadpoles of the native Australian frog Limnodynastes peronii were exposed to Se in both forms, and live-animal gamma spectroscopy was used to track accumulation and retention over time. Tissue biodistributions were also quantified at the end of the uptake and depuration phases. Results showed the bioconcentration of SeIV to be 3 times greater compared to SeVI, but rates of elimination were similar for both forms. This suggests a change of Se speciation within the organism prior to excretion. Depuration kinetics were best described by a one-phase exponential decay model, and tadpoles retained approximately 19% of the accumulated Se after 12 days of depuration in clean water. Selenium bioaccumulation was greatest in digestive and excretory organs, as well as the eye, which may directly relate to previously reported Se-induced impairments. Results demonstrate how the use of radiotracing techniques can significantly improve our understanding of trace element toxicokinetics and tissue distributions in developing amphibians. From an environmental monitoring perspective, the findings highlight the importance of considering chemical speciation as this could influence the accuracy of risk assessment. [ABSTRACT FROM AUTHOR]