Organisms are able to control metal concentrations in certain tissues of their body to minimize damage of reactive forms of essential and nonessential metals and to control selective utilization of essential metals. These physiological aspects of organisms are not accounted for when assessing the risk of metals in the environment. The Critical Body Residue (CBR) approach relates toxicity to bioaccumulation and biomagnification and might at first sight provide a more accurate estimation of effects than the external concentration. When expressing CBRs on total internal concentrations, the capacity of organisms to sequester metals in forms that are not biologically reactive is neglected. The predictability of toxic effects will increase when knowledge on metal compartmentalization within the organisms' body is taken into account. Insight in metal compartmentalization sheds light on the different accumulation strategies organisms can follow upon metal exposure. Using a fractionation procedure to isolate metal-rich granules and tissue fragments from intracellular and cytosolic fractions, the internal compartmentalization of metals can be approximated. In this paper, current knowledge regarding metal compartmentalization in organisms is summarized, and metal fractions are identified that are indicators of toxicity. Guidance is provided on future improvement of models, such as the Biotic Ligand Model (BLM), for risk assessment of metal stress to biota.

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Microplastics are ubiquitous in the environment, are frequently ingested by organisms, and may potentially cause harm. A range of studies have found significant levels of microplastics in beach sand. However, there is a considerable amount of methodological variability among these studies. Methodological variation currently limits comparisons as there is no standard procedure for sampling or extraction of microplastics. We identify key sampling and extraction procedures across the literature through a detailed review. We find that sampling depth, sampling location, number of repeat extractions, and settling times are the critical parameters of variation. Next, using a case-study we determine whether and to what extent these differences impact study outcomes. By investigating the common practices identified in the literature with the case-study, we provide a standard operating procedure for sampling and extracting microplastics from beach sand.

Here we present the large-scale distribution of microplastic contamination in beach sediment across Europe. Sediment samples were collected from 23 locations across 13 countries by citizen scientists, and analysed using a standard operating procedure. We found significant variability in the concentrations of microplastics, ranging from 72±24 to 1512±187 microplastics per kg of dry sediment, with high variability within sampling locations. Three hotspots of microplastic accumulation (>700 microplastics per kg of dry sediment) were found. There was limited variability in the physico-chemical characteristics of the plastics across sampling locations. The majority of the microplastics were fibrous, <1mm in size, and blue/black in colour. In addition, using Raman spectrometry we identified particles as polyester, polyethylene, and polypropylene. Our research is the first large spatial-scale analysis of microplastics on European beaches giving insights into the nature and extent of the microplastic challenge.