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Accepted manuscript. Final version published in Environmental Science & Technology, 53(4), 1834-1843, is available at https://doi.org/10.1021/acs.est.8b06399. Temporally (1965–2015) and spatially (55°–70°N) extensive records of total mercury (Hg) in freshwater fish showed consistent declines in boreal and subarctic Fennoscandia. The database contains 54 560 fish entries (n: pike > perch ≫ brown trout > roach ≈ Arctic charr) from 3132 lakes across Sweden, Finland, Norway, and Russian Murmansk area. 74% of the lakes did not meet the 0.5 ppm limit to protect human health. However, after 2000 only 25% of the lakes exceeded this level, indicating improved environmental status. In lakes where local pollution sources were identified, pike and perch Hg concentrations were significantly higher between 1965 and 1990 compared to values after 1995, likely an effect of implemented reduction measures. In lakes where Hg originated from long-range transboundary air pollution (LRTAP), consistent Hg declines (3–7‰ per year) were found for perch and pike in both boreal and subarctic Fennoscandia, suggesting common environmental controls. Hg in perch and pike in LRTAP lakes showed minimal declines with latitude, suggesting that drivers affected by temperature, such as growth dilution, counteracted Hg loading and food web exposure. We recommend that future fish Hg monitoring sampling design should include repeated sampling and collection of pollution history, water chemistry, fish age, and stable isotopes to enable evaluation of emission reduction policies.

Despite global efforts to reduce anthropogenic mercury (Hg) emissions, the timescale and degree to which Hg concentrations in the environment and biota respond to decreased emissions remain challenging to assess or predict. In the present study we characterize long-term trends and life-history patterns in Hg accumulation and toxicological implications of Hg contamination for a freshwater seal from one of the world's largest lakes (Lake Baikal, Siberia, Russia) using contemporary tissues and archival teeth. Stable isotope analysis and Hg analyses of soft tissues (muscle, liver, kidney, blood, brain, heart) and teeth from 22 contemporary seals revealed rapid changes in diet and Hg accumulation in the first year of life with a stable diet and increase in tissue Hg throughout the rest of life. Although maternal transfer of Hg was an important source of Hg to seal pups, reproduction and lactation by female seals did not appear to result in sex-related differences in Hg concentrations or age-related accumulation in adult seals. Based on Hg analysis of archival teeth (n = 114) and reconstructed values for soft tissues, we also assessed temporal trends in seal Hg between the years 1960 and 2013. Seal Hg concentrations in hard (teeth) and soft (e.g., muscle, liver) tissues were highest in the 1960s and 1970s, followed by a decrease. The decline in seal Hg concentrations in recent decades was most likely driven by a reduction in Hg inputs to the lake, suggesting that global and regional efforts to reduce Hg emissions have been successful at reducing ecosystem and human health risks posed by Hg in Lake Baikal. Environ Toxicol Chem 2018;37:1476-1486. © 2018 SETAC.

Considerable amounts of previously deposited persistent organic pollutants (POPs) are stored in the Arctic cryosphere. Transport of freshwater and terrestrial material to the Arctic Ocean is increasing due to ongoing climate change and the impact this has on POPs in marine receiving systems is unknown This study has investigated how secondary sources of POPs from land influence the occurrence and fate of POPs in an Arctic coastal marine system. Passive sampling of water and sampling of riverine suspended particulate matter (SPM) and marine sediments for analysis of polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB) was carried out in rivers and their receiving fjords in Isfjorden system in Svalbard. Riverine SPM had low contaminant concentrations (14, 16–100 pg/g dw HCB) compared to outer marine sediments 630-880 pg/g dw ΣPCB14, 530–770 pg/g dw HCB). There was a strong spatial gradient in sediment PCB and HCB concentrations with lowest concentrations in river estuaries and in front of marine-terminating glaciers and increasing concentrations toward the outer fjord. This suggests that rather than leading to increased concentrations, inputs of SPM from land lead to a dilution of contaminant concentrations in nearshore sediments. Preliminary estimates of SPM:water activity ratios suggest that terrestrial particles (with low contaminant concentrations) may have the potential to act as sorbents of dissolved contaminants in the coastal water column, with implications for bioavailability of POPs to the marine food web. There is concern that ongoing increases in fluxes of freshwater, sediments and associated terrestrial material (including contaminants) from land to the Arctic Ocean will lead to increased mobilization and transport of POPs to coastal ecosystems. However, the results of this study indicate that on Svalbard, inputs from land may in fact have the opposite effect, leading to reduced concentrations in coastal sediments and waters.

Methylmercury (MeHg) concentrations in freshwater fish from southeastern Norway continue to increase, highlighting the need for a comprehensive understanding of MeHg sources, cycling, and degradation in the aquatic environment. The authors assessed the importance of photodemethylation in the MeHg budget of 4 Norwegian lakes. Photodemethylation rates were determined using incubation experiments with MeHg-spiked natural lake water. The authors determined full-spectrum exposure rates at all study sites and waveband-specific rates (photosynthetically active radiation, ultraviolet-A radiation, and ultraviolet-B radiation) at 1 clear-water (Sognsvann) and 1 humic (Langtjern) site. No significant differences in photodemethylation rates between the sites were found, and the authors' observed rates agreed with available literature for lake and wetland waters. The authors paired experimentally derived photodemethylation rates with lake-specific incident irradiation, light attenuation, and MeHg concentrations to estimate MeHg loss through photodemethylation for the study sites. For Langtjern, losses through photodemethylation equalled 27% of total annual inputs, highlighting the importance of photodemethylation in the MeHg budget. Furthermore, the authors assessed how changes in terrestrial dissolved organic carbon (DOC) exported to freshwaters and climate-driven reductions in ice cover duration may affect MeHg losses through photodemethylation. Results suggest that future increases in DOC may lead to higher aqueous MeHg concentrations in boreal lakes due to increased DOC-associated MeHg inputs paired with significant decreases in the loss of MeHg through photodemethylation due to increased light attenuation. Environ Toxicol Chem 2015;34:1213–1223. © 2015 SETAC

This review compiles available information on the concentrations, sources, fate and toxicity of amines and amine-related compounds in surface waters, including rivers, lakes, reservoirs, wetlands and seawater. There is a strong need for this information, especially given the emergence of amine-based post-combustion CO2 capture technologies, which may represent a new and significant source of amines to the environment. We identify a broad range of anthropogenic and natural sources of amines, nitrosamines and nitramines to the aquatic environment, and identify some key fate and degradation pathways of these compounds. There were very few data available on amines in surface waters, with reported concentrations often below detection and only rarely exceeding 10 μg/L. Reported concentrations for seawater and reservoirs were below detection or very low, while for lakes and rivers, concentrations spanned several orders of magnitude. The most prevalent and commonly detected amines were methylamine (MA), dimethylamine (DMA), ethylamine (EA), diethylamine (DEA) and monoethanolamine (MEAT). The paucity of data may reflect the analytical challenges posed by determination of amines in complex environmental matrices at ambient levels. We provide an overview of available aquatic toxicological data for amines and conclude that at current environmental concentrations, amines are not likely to be of toxicological concern to the aquatic environment, however, the potential for amines to act as precursors in the formation of nitrosamines and nitramines may represent a risk of contamination of drinking water supplies by these often carcinogenic compounds. More research on the prevalence and toxicity of amines, nitrosamines and nitramines in natural waters is necessary before the environmental impact of new point sources from carbon capture facilities can be adequately quantified.

In the present preliminary study, the authors identify 2 pathways through which invasive dreissenid mussels can transfer microcystin to higher trophic levels: either directly, through consumption by benthivorous fish such as the round goby; or indirectly, through their biodeposits, which are an important food source for benthic invertebrates. The results suggest that dreissenid mussels represent a potentially important benthic pathway for the food web transfer of microcystin. Environ Toxicol Chem 2013;32:2159–2164. © 2013 SETAC

We investigated the factors influencing cyanobacterial biomass and microcystin (MC) concentrations in several Ugandan lakes from September 2008 to February 2009. We characterized thermal structure, light availability, nutrient concentrations, chlorophyll a, phytoplankton d13C (as an indicator of CO2 limitation), and phytoplankton community composition and abundance as well as MC concentrations. We used these data to test several hypotheses based on previous research in temperate lakes regarding the factors that encourage high cyanobacterial biomass and MC concentrations. Site characteristics that appeared to favor high cyanobacterial biomass (especially Microcystis) included: high total phosphorus concentrations, low total nitrogen to total phosphorus (TN:TP) ratios, and possibly low CO2 availability. Light availability, total nitrogen concentrations, and thermal structure of the water column were not related to cyanobacterial biomass. MC concentrations were strongly related to Microcystis biomass (and were not related to the biomass of any other cyanobacterial taxa), which was positively correlated with total phosphorus and chlorophyll a concentrations. MC cell content may be moderated by CO2 availability, with MC cell quotas tending to be lower where the potential for C-limitation of photosynthesis was higher. In these phosphorus-rich tropical lakes, the shallowest study sites were most conducive to the development of large standing crops of Microcystis and high MC concentrations. The environmental conditions that appear to favor high cyanobacterial biomass and MC concentrations in our Ugandan study lakes are similar to what has been observed for temperate lakes.

Nearshore regions of lakes are important sources of fish, and can be strongly influenced by anthropogenic inputs of nutrients as well as contaminants. This study characterizes food web structure, mercury concentrations, and biomagnification of mercury in two embayments in northern Lake Victoria that differ in their connectivity to the open lake, trophic status, and the influence of local anthropogenic pollution. Murchison Bay is a semi-confined hypereutrophic bay in a densely populated region, while Napoleon Gulf is mesotrophic and is well flushed with water from the open lake. Based on stable carbon and nitrogen isotope analysis, food web structure was similar at both sites, with short food chains and conspecific fish occupying similar trophic positions. However, there were strong differences in net phytoplankton δ 15 N and δ 13 C between sites; net phytoplankton δ 13 C was largely related to trophic status, while δ 15 N values appeared to be influenced by inputs of human waste and the prevalence of biological nitrogen fixation. Total mercury (THg) concentrations in fish were consistently below 200 ng/g wet weight, and despite elevated THg concentrations in water in Murchison Bay, THg concentrations in net phytoplankton and fish from both embayments did not differ, highlighting that THg in water is not always a good predictor of concentrations in fish. We also observed that biomagnification of mercury was occurring at a lower rate in Murchison Bay than in Napoleon Gulf, and we propose that the hypereutrophic state of Murchison Bay may be acting to reduce potential Hg exposure for higher trophic level fish.

Lake sediment cores have been used to reconstruct mercury deposition patterns in many parts of the world; however, no studies to date have used these methods in West Africa, nor are there any published measurements of mercury deposition to this region. We measured mercury in a 210 Pb dated sediment core from a meromictic crater lake in West Africa (Lake Bosomtwe, Ghana). Lake Bosomtwe has a very small catchment area to lake area ratio (1.1) and the sediment mercury profile is expected to reflect past and present atmospheric mercury deposition to the lake. Mercury concentrations in sediments as well as mercury flux to the sediments increased from the mid-1800s to latter half of the 1900s, however there has been a sharp decline in mercury flux to Lake Bosomtwe in recent decades. The recent decline in mercury flux to Lake Bosomtwe's sediments does not appear to be consistent with trends in local, regional or global mercury emissions, and may instead reflect declining global atmospheric mercury concentrations or declining European emissions, highlighting the importance of long-range atmospheric transport of mercury.