Evidence is accumulating that sorption of organic chemicals to soils and sediments can be described by "dual-mode sorption": absorption in amorphous organic matter (AOM) and adsorption to carbonaceous materials such as black carbon (BC), coal, and kerogen, collectively termed "carbonaceous geosorbents" (CG). Median BC contents as a fraction of total organic carbon are 9% for sediments (number of sediments, n approximately 300) and 4% for soils (n = 90). Adsorption of organic compounds to CG is nonlinear and generally exceeds absorption in AOM by a factor of 10-100. Sorption to CG is particularly extensive for organic compounds that can attain a more planar molecular configuration. The CG adsorption domain probably consists of surface sites and nanopores. In this review it is shown that nonlinear sorption to CG can completely dominate total sorption at low aqueous concentrations (<10(-6) of maximum solid solubility). Therefore, the presence of CG can explain (i) sorption to soils and sediments being up to 2 orders of magnitude higher than expected on the basis of sorption to AOM only (i.e., "AOM equilibrium partitioning"), (ii) low and variable biota to sediment accumulation factors, and (iii) limited potential for microbial degradation. On the basis of these consequences of sorption to CG, it is advocated that the use of generic organic carbon-water distribution coefficients in the risk assessment of organic compounds is not warranted and that bioremediation endpoints could be evaluated on the basis of freely dissolved concentrations instead of total concentrations in sediment/soil.

Microplastics have recently been detected in drinking water as well as in drinking water sources. This presence has triggered discussions on possible implications for human health. However, there have been questions regarding the quality of these occurrence studies since there are no standard sampling, extraction and identification methods for microplastics. Accordingly, we assessed the quality of fifty studies researching microplastics in drinking water and in its major freshwater sources. This includes an assessment of microplastic occurrence data from river and lake water, groundwater, tap water and bottled drinking water. Studies of occurrence in wastewater were also reviewed. We review and propose best practices to sample, extract and detect microplastics and provide a quantitative quality assessment of studies reporting microplastic concentrations. Further, we summarize the findings related to microplastic concentrations, polymer types and particle shapes. Microplastics are frequently present in freshwaters and drinking water, and number concentrations spanned ten orders of magnitude (1 × 10 −2 to 10 8 #/m 3 ) across individual samples and water types. However, only four out of 50 studies received positive scores for all proposed quality criteria, implying there is a significant need to improve quality assurance of microplastic sampling and analysis in water samples. The order in globally detected polymers in these studies is PE ≈ PP > PS > PVC > PET, which probably reflects the global plastic demand and a higher tendency for PVC and PET to settle as a result of their higher densities. Fragments, fibres, film, foam and pellets were the most frequently reported shapes. We conclude that more high quality data is needed on the occurrence of microplastics in drinking water, to better understand potential exposure and to inform human health risk assessments.

Recent studies have shown that sorption of polycyclic aromatic hydrocarbons (PAHs) in soot-water systems is exceptionally strong. As a consequence, soot may fully control the actual fate of PAHs in the aquatic environment. However, sorption has only been characterized for a limited number of PAHs to diesel soot, and the mechanism is poorly understood. In this paper, we present an extensive data set of sorbent-water distribution coefficients (K(S), n = 236) for a series of PAHs (both native and added) and polychlorinated biphenyls (PCBs) to five different types of soot and five soot-like materials. Both Ks values and physicochemical properties of the sorbents show large variation. In general, sorption is very strong, with K(S) values up to 10(10), showing the highest distribution coefficients on a mass basis ever reported. Sorption of in particular PAHs is often over 1000 times as strong as sorption to amorphous sedimentary organic carbon. The variation in K(S) values cannot be explained by "soot carbon fractions" or specific surface areas of the sorbents. Instead, values for native PAHs are mostly determined by the sorbates' molar volume, and values for added PAHs and PCBs are determined by the sorbents' average pore diameter. From differences in K(S) values between native and added PAH analogues, it can be deduced that generally more than 50% (with values up to 97%) of the native PAH concentration in soot is not available for distribution to the aqueous phase. We conclude that this is caused by physical entrapment of the chemicals within the solid matrix. Furthermore, most sorbents appear to preferentially sorb PCBs with planar configurations, a phenomenon most likely driven by sorption in molecular-sized pores. Pore sorption is also concluded to be the most important sorption mechanism for added PAHs together with pi-pi interaction processes with flat aromatic sorbent surfaces. Frequently observed, slowly desorbing, resistant contaminant fractions in sediments may very well be explained on the basis of these results.

The hypothesis that 'microplastic will transfer hazardous hydrophobic organic chemicals (HOC) to marine animals' has been central to the perceived hazard and risk of plastic in the marine environment. The hypothesis is often cited and has gained momentum, turning it into paradigm status. We provide a critical evaluation of the scientific literature regarding this hypothesis. Using new calculations based on published studies, we explain the sometimes contrasting views and unify them in one interpretive framework. One explanation for the contrasting views among studies is that they test different hypotheses. When reframed in the context of the above hypothesis, the available data become consistent. We show that HOC microplastic-water partitioning can be assumed to be at equilibrium for most microplastic residing in the oceans. We calculate the fraction of total HOC sorbed by plastics to be small compared to that sorbed by other media in the ocean. We further demonstrate consistency among (a) measured HOC transfer from microplastic to organisms in the laboratory, (b) measured HOC desorption rates for polymers in artificial gut fluids (c) simulations by plastic-inclusive bioaccumulation models and (d) HOC desorption rates for polymers inferred from first principles. We conclude that overall the flux of HOCs bioaccumulated from natural prey overwhelms the flux from ingested microplastic for most habitats, which implies that microplastic ingestion is not likely to increase the exposure to and thus risks of HOCs in the marine environment.

It has been speculated that marine microplastics may cause negative effects on benthic marine organisms and increase bioaccumulation of persistent organic pollutants (POPs). Here, we provide the first controlled study of plastic effects on benthic organisms including transfer of POPs. The effects of polystyrene (PS) microplastic on survival, activity, and bodyweight, as well as the transfer of 19 polychlorinated biphenyls (PCBs), were assessed in bioassays with Arenicola marina (L.). PS was pre-equilibrated in natively contaminated sediment. A positive relation was observed between microplastic concentration in the sediment and both uptake of plastic particles and weight loss by A. marina. Furthermore, a reduction in feeding activity was observed at a PS dose of 7.4% dry weight. A low PS dose of 0.074% increased bioaccumulation of PCBs by a factor of 1.1-3.6, an effect that was significant for ΣPCBs and several individual congeners. At higher doses, bioaccumulation decreased compared to the low dose, which however, was only significant for PCB105. PS had statistically significant effects on the organisms' fitness and bioaccumulation, but the magnitude of the effects was not high. This may be different for sites with different plastic concentrations, or plastics with a higher affinity for POPs.