Microplastics (MPs) pollution in Tangxun Lake, the largest urban lake in China, was investigated. The average MPs pollution in sediment (1.81 ± 1.75 × 10⁴ items kg⁻¹) is at a high level, while the MPs in lakeshore water (917.77 ± 742.17 items m⁻³) is in the middle to low level compared with existing studies, which is related to the government's protection. Fragments and fibers are the most common shapes in sediment and water, respectively. MPs size <1 mm dominates in the sediment, while the MPs in water has a larger size. The distribution of MPs in the inner lake shows that pellets tend to “hidden” in sediments. Suspected MPs are randomly selected for polymer detection by Micro-Raman microscopy. Polypropylene (PP), polyethylene (PE) and polyethylene terephthalate (PET) are the most common polymer types in water, sediment and atmospheric deposition MPs samples. The input of wastewater, fishery and surrounding human activities are the main sources of MPs in sediment. Atmospheric deposition has a great impact on the distribution of MPs, while the contribution of surface runoff to lake MPs is not remarkable. In addition, MPs in sediments have exceeded the environmental carrying capacity. More attention should be focused on the sediment, where huge amounts of MPs are “hidden”.

Sewage sludge used as agricultural fertilizer has been identified as an important source of microplastics (MPs) to the environment. However, the fate of MPs added to agricultural soils is largely unknown. This study investigated the fate of MPs in agricultural soils amended with sewage sludge and the role of surface water runoff as a mechanism driving their transfer to aquatic ecosystems. This was assessed using three experimental plots located in a semi-arid area of Central Spain, which were planted with barley. The experimental plots received the following treatments: (1) control or no sludge application; (2) historical sludge application, five years prior to the experiment; and (3) sludge application at the beginning of the experiment. MPs were analyzed in surface water runoff and in different soil layers to investigate transport and infiltration for one year. The sewage sludge used in our experiment contained 5972–7771 MPs/kg dw. Based on this, we estimated that about 16,000 MPs were added to the agricultural plot amended with sludge. As expected, the sludge application significantly increased the MP concentration in soils. The control plot contained low MP concentrations (31–120 MPs kg⁻¹ dw), potentially originating from atmospheric deposition. The plot treated five years prior to the experiment contained 226–412 and 177–235 MPs kg⁻¹ dw at the start and end of the experiment, respectively; while the recently treated plot contained 182–231 and 138–288 MPs kg⁻¹ dw. Our study shows that MP concentrations remain relatively constant in agricultural soils and that the MP infiltration capacity is very low. Surface water runoff had a negligible influence on the export of MPs from agricultural soils, mobilizing only 0.2–0.4% of the MPs added with sludge. We conclude that, in semi-arid regions, agricultural soils can be considered as long-term accumulators of MPs.

Salt marsh estuaries serve as sources and sinks for nutrients and elements to and from estuarine water, which enhances and alleviates watershed fluxes to the coastal ocean. We assessed sources and sinks of mercury in the intertidal Plum Island Sound estuary in Massachusetts, the largest salt marsh estuary of New England, using 25-km spatial water sampling transects. Across all seasons, dissolved (FHg) and total (THg) mercury concentrations in estuarine water were highest and strongly enhanced in upper marshes (1.31 ± 0.20 ng L⁻¹ and 6.56 ± 3.70 ng L⁻¹, respectively), compared to riverine Hg concentrations (0.86 ± 0.17 ng L⁻¹ and 0.88 ± 0.34 ng L⁻¹, respectively). Mercury concentrations declined from upper to lower marshes and were lowest in ocean water (0.38 ± 0.10 ng L⁻¹ and 0.56 ± 0.25 ng L⁻¹, respectively). Conservative mixing models using river and ocean water as endmembers indicated that internal estuarine Hg sources strongly enhanced estuarine water Hg concentrations. For FHg, internal estuarine Hg contributions were estimated at 26 g yr⁻¹ which enhanced Hg loads from riverine sources to the ocean by 44%. For THg, internal sources amounted to 251 g yr⁻¹ and exceeded riverine sources six-fold. Proposed sources for internal estuarine mercury contributions include atmospheric deposition to the large estuarine surface area and sediment re-mobilization, although sediment Hg concentrations were low (average 23 ± 2 μg kg⁻¹) typical of uncontaminated sediments. Soil mercury concentrations under vegetation, however, were ten times higher (average 200 ± 225 μg kg⁻¹) than in intertidal sediments suggesting that high soil Hg accumulation might drive lateral export of Hg to the ocean. Spatial transects of methylated Hg (MeHg) showed no concentration enhancements in estuarine water and no indication of internal MeHg sources or formation. Initial mass balance considerations suggest that atmospheric deposition may either be in similar magnitude, or possibly exceed lateral tidal export which would be consistent with strong Hg accumulation observed in salt marsh soils sequestering Hg from current and past atmospheric deposition.

Microplastics are contaminants that are closely associated with human activity and are often abundant even in remote areas. As the largest natural freshwater lake in the western USA, Flathead Lake is a suitable site to study microplastics in lakes in less-populated areas of North America. Our assessment of microplastics in lake surface water samples showed that microplastic densities and concentrations in Flathead Lake were similar to those in other lakes located in less-populated areas around the world, with densities ranging from 8.00 × 10⁴ to 4.22 × 10⁵ particles/km² with a mean concentration of 1.89 × 10⁵ particles/km². Dry deposition rates for microplastics ranged from 4 to 140 particles/m²/day with an average of 69 particles/m²/day and were significantly higher in the fall. Microplastic concentrations in wet deposition ranged from 0.006 particles/mL to 0.050 particles/mL with highest concentrations in winter and lowest in summer. Fibrous microplastics were predominant in both lake water and atmospheric deposition. The high densities of microplastics in the sample sites located near the Flathead River inlet suggests that the river is an important source of microplastics to Flathead Lake. The high densities of microplastics and high proportions of non-fibrous microplastics near populated areas of the lake imply that local human activities also affect microplastics in Flathead Lake. Although the annual flux of microplastics in dry deposition was higher than that in wet deposition, the relatively modest difference suggests that precipitation might enhance the deposition of microplastics. The results of this study indicate that instituting increased control measures that target both reducing the microfibers generated by laundry and improving the overall level of plastic waste management in the watershed may help in controlling microplastic levels in Flathead Lake.

The coastal megacity Shanghai is located in the center of the Yangtze River Delta, a dominant flame retardants (FRs) production region in China, especially for organophosphate esters (OPEs). This prompted us to investigate occurrence and seasonal changes of atmospheric OPEs in Shanghai, as well as to evaluate their sources, environmental behavior and fate as a case study for global coastal regions. Atmospheric gas and particle phase OPEs were weekly collected at two coastal sites - the emerging town Lingang New Area (LGNA), and the chemical-industry zone Jinshan Area (JSA) from July 2016–June 2017. Total atmospheric concentrations of the observed OPEs were significantly higher in JSA (median of 1800 pg m⁻³) than LGNA (median of 580 pg m⁻³). Tris(1-chloro-2-propyl) phosphate (TCPP) was the most abundant compound, and the proportion of three chlorinated OPEs were higher in the particle phase (55%) than in the gas phase (39%). The year-round median contribution of particle phase OPEs was 33%, which changed strongly with seasons, accounting for 10% in summer in contrast to 62% in winter. Gas and particle phase OPEs in JSA exhibited significant correlations with inverse of temperature, respectively, indicating the importance of local/secondary volatilization sources. The estimated fluxes of gaseous absorption were almost 2 orders of magnitude higher than those of particle phase deposition, which could act as sources of organic phosphorus to coastal and open ocean waters.

The Yellow River Delta (YRD) wetland, the most important estuary wetland in eastern China, has an important ecosystem service function. Rapid and intensive development has inevitably led to the accumulation of potentially toxic elements (PTEs) in soils. Therefore, identifying quantitative sources and spatial distributions of PTEs is essential for soil environmental protection in the YRD. A total of 240 topsoil samples (0–20 cm) were collected in the Yellow River Delta Nature Reserve (YRDNR) and analyzed the PTE contents. To avoid the biases of the single receptor model, positive matrix factorization, factor analysis with nonnegative constraints, and maximum likelihood principal component analysis-multivariate curve resolution-alternating least squares were used for source apportionment of soil PTEs. To promote the efficiency of multivariate geostatistical simulation, a minimum/maximum autocorrelation factor-sequential Gaussian simulation was built to map the spatial patterns of PTEs. Three factors were derived by the three receptor models, and their contributions to the source explanation were similar. As, Cr, Cu, Mn, Ni, and Zn originated from natural sources, with contributions of 85.6%–96.4 %. A total of 61.5 % of Hg was associated with atmospheric deposition of coal combustion and wastewater from upstream. Agricultural activities and oil exploitation contributed 33.5 % and 15.9 % of the Cd and Pb concentrations. Spatial distributions of soil PTEs were controlled by sedimentary grain size. A total of 47.2 % of the total study area was identified as hazardous area for Cd, 10.3 % for As, and 5.4 % for Hg. This work is expected to provide references for soil pollution assessment and management of YRDNR.

Mercury (Hg) is a neurotoxic element with severe effects on humans and wildlife. Widely distributed by atmospheric deposition, it can also be localized near point sources such as mines. Mercury has been shown to reduce the reproduction of bird populations in field observations in North America and Europe, but studies are needed in Asia, where the majority of emissions now occur. We investigated the reproduction of two passerines, Japanese Tit (Parus minor) and Russet Sparrow (Passer rutilans), in a large-scale Hg mining district, and a non-mining district, both in Guizhou, southwest China. Concentrations of Hg were elevated in the mining district (blood levels of 2.54 ± 2.21 [SD] and 0.71 ± 0.40 μg/g, in adult tits and sparrows, respectively). However, we saw no evidence of decreased breeding there: metrics such as egg volume, nestling weight, hatching and fledgling success, were all similar between the different districts across two breeding seasons. Nor were there correlations at the mining district between Hg levels of adults or juveniles, and hatching or fledgling success, or nestling weight. Nest success was high even in the mining district (tit, 64.0%; sparrow: 83.1%). This lack of reproductive decline may be related to lower blood levels in nestlings (means < 0.15 μg/g for both species). Concentrations of selenium (Se), and Se-to-Hg molar ratio, were also not correlated to breeding success. Although blood levels of 3.0 μg/g have been considered as a threshold of adverse effects in birds, even leading to severe effects, we detected no population-level reproductive effects, despite ~25% of the adult tits being above this level. Future work should investigate different locations in the mining district, different life-stages of the birds, and a wider variety of species. The hypothesis that bird populations can evolve resistance to Hg in contaminated areas should also be examined further.

In this review, global change processes have been linked to polycyclic aromatic compounds (PACs) in Canada and a first national budget of sources and sinks has been derived. Sources are dominated by wildfire emissions that affect western and northern regions of Canada disproportionately due to the location of Pacific and boreal forests and the direction of prevailing winds. Wildfire emissions are projected to increase under climate warming along with releases from the thawing of glaciers and permafrost. Residential wood combustion, domestic transportation and industry contribute the bulk of anthropogenic emissions, though they are substantially smaller than wildfire emissions and are not expected to change considerably in coming years. Other sources such as accidental spills, deforestation, and re-emission of previous industrial deposition are expected to contribute anthropogenic and biogenic PACs to nearby ecosystems. PAC sinks are less well-understood. Atmospheric deposition is similar in magnitude to anthropogenic sources. Considerable knowledge gaps preclude the estimation of environmental transformations and transboundary flows, and assessing the importance of climate change relative to shifts in population distribution and energy production is not yet possible. The outlook for PACs in the Arctic is uncertain due to conflicting assessments of competing factors and limited measurements, some of which provide a baseline but have not been followed up in recent years. Climate change has led to an increase in primary productivity in the Arctic Ocean, but PAC-related impacts on marine biota appear to be modest. The net effect of changes in ecological exposure from changing emissions and environmental conditions throughout Canada remains to be seen. Evidence suggests that the PAC budget at the national scale does not represent impacts at the local or regional level. The ability to assess future trends depends on improvements to Canada’s environmental measurement strategy and biogeochemical modelling capability.

Inputs of polycyclic aromatic hydrocarbons (PAHs) of regulatory interest from diffuse atmospheric sources within urban areas frequently elevate local soil concentrations to levels requiring remediation despite the lack of in-situ contamination. This research sought to determine the distribution and potential health effects of aerially deposited PAHs in soil within the urban core of metropolitan Milwaukee, Wisconsin, U.S.A. as part of a soil regulatory standards reevaluation. Park areas (n = 27) identified as undisturbed for 80+ years, containing no fill material, and receiving only atmospheric deposition were selected for composite surface and 92 cm core soil sample collection (n = 295). Samples were analyzed for the 16 USEPA priority PAHs, 1- and 2- methylnapthalene and ancillary soil properties. Soil core and ancillary data confirm lack of site disturbance. PAH diagnostic ratios and homologue summations indicate that diffuse multiple point source emissions contribute equally to PAH deposition throughout the area. Benzo(a)pyrene (BaP) and dibenz(a,h)anthracene mean concentrations exceed health-based clean up levels. Risk assessment shows only a worst-case exposure scenario (BaP at the 95% upper confidence limit) increasing cancer risk (1.67 × 10⁻⁶) over current regulatory thresholds (1.0 × 10⁻⁶). Health quotients show potential health risks from fluoranthene and pyrene for daily park users and from BaP for all others. Mean soil PAH values are similar to New Orleans, but lower than Chicago, Boston, and London reflecting industrial history and site selection protocols. The soil PAH results presented here for sites selected for non-manipulated soils combined with an almost 100-year uninterrupted atmospheric exposure effectively show the maximum potential PAH values that can be found at any given undisturbed location within the Milwaukee urban core due solely to atmospheric deposition.

Critical loads are thresholds of atmospheric deposition below which harmful ecological effects do not occur. Because lichens are sensitive to atmospheric deposition, lichen-based critical loads can foreshadow changes of other forest processes. Here, we derive critical loads of nitrogen (N) and sulfur (S) deposition for continental US and coastal Alaskan forests, based on nationally consistent lichen community surveys at 8855 sites. Across the eastern and western US ranges of 459 lichen species, each species' realized optimum was the N or S atmospheric deposition value at which it most frequently occurred. The mean of optima for all species at a site, weighted by their abundances, was defined as a community “airscore” indicative of species’ collective responses to atmospheric deposition. To determine critical loads for adverse community compositional shifts, we then modeled changes in airscores as a function of deposition, climate and forest habitat predictors in nonparametric multiplicative regression. Critical loads, indicative of initial shifts from pollution-sensitive toward pollution-tolerant species, occurred at 1.5 kg N ha⁻¹ y⁻¹ and 2.7 kg S ha⁻¹ y⁻¹. Importantly, these critical loads remain constant under any climate regime nationwide, suggesting both simplicity and nationwide applicability. Our models predict that preventing excess N deposition of just 0.2–2.0 kg ha⁻¹ y⁻¹ in the next century could offset the detrimental effects of predicted climate warming on lichen communities. Because excess deposition and climate warming both harm the most ecologically influential species, keeping conditions below critical loads would sustain both forest ecosystem functioning and climate resilience.