International audience | This study addressed the relative importance of particle coating, sewage sludge amendment, and aging on aggregation and dissolution of manufactured Ag nanoparticles (Ag MNPs) in soil pore water. Ag MNPs with citrate (CIT) or polyvinylpyrrolidone (PVP) coatings were incubated with soil or municipal sewage sludge which was then amended to soil (1% or 3% sludge (w/w)). Pore waters were extracted after 1 week and 2 and 6 months and analyzed for chemical speciation, aggregation state and dissolution. Ag MNP coating had profound effects on aggregation state and partitioning to pore water in the absence of sewage sludge, but pre-incubation with sewage sludge negated these effects. This suggests that Ag MNP coating does not need to be taken into account to understand fate of AgMNPs applied to soil through biosolids amendment. Aging of soil also had profound effects that depended on Ag MNP coating and sludge amendment. (C) 2013 Elsevier Ltd. All rights reserved.

Dissolved organic matter (DOM) plays a significant role in the photochemical behavior of nano- and micro-plastic particles (NPs/MPs). We investigated the influence of DOM on the mechanism on the photoaging of NPs/MPs with different molecular structures under UV₃₆₅ irradiation in water. DOM components used in this study are mainly humic acid and fulvic acid. The results showed that DOM promoted the weathering of aliphatic NPs/MPs (polypropylene (PP)), but inhibited or had only a minor effect on the photoaging of aromatic NPs/MPs (polystyrene (PS) NPs/MPs, carboxyl-modified PS NPs, amino-modified PS NPs, and polycarbonate MPs). NPs with a large surface area may adsorb sufficient DOM on the particle surfaces through π-π interactions, which competes with NPs for photon absorption sites, thus, can delay the photoaging of PS NPs. Aromatic MPs may release phenolic compounds that quench •OH, thereby weakening the photoaging process. For aliphatic MPs, the detection of peracid, aldehyde, and ketone groups on the polymer surface indicated that DOM promoted weathering of PP MPs, which was primarily because the generation of •OH due to DOM photolysis may attack the polymer by C–C bond cleavage and hydrogen extraction reactions. This study provides insight into the UV irradiation weathering process of NPs/MPs of various compositions and structures, which are globally distributed in water.

A large amount of plastic waste is generated yearly worldwide, and landfills are commonly used for the disposal of plastic waste. However, burying in landfill does not get rid of the plastic waste but leave the problem to the future. Previous works have showed that microplastics are presented in the landfill refuse and leachate, which might be potential sources of microplastics. In this work, characteristics of microplastic pollution in an informal landfill in South China were studied. Landfill refuse, underlying soil, leachate, and groundwater samples were collected from different sites within and around the landfill. Results show that microplastics in the landfill refuse and underlying soil varied from 590 to 103,080 items/kg and from 570 to 14,200 items/kg, respectively. Most of the microplastics are fibrous, small sized, and transparent. Polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) are major polymer types. Scanning electron microscope (SEM) images and Fourier Transform Infrared (FTIR) spectra of the microplastic samples indicate varying degree of weathering. Microplastic abundances in the landfill leachate and groundwater ranged from 3 to 25 items/L and from 11 to 17 items/L, respectively. Microplastics detected in the landfill leachate and groundwater are even smaller compared with those in the refuse and underlying soil and their polymer types are more diverse. This work demonstrated that microplastics presented in an informal landfill without sufficient protection can leak out to the surrounding environment. The microplastic pollution originated from informal landfills should receive more attentions.

The landfills store a lot of waste plastics, thus it has been confirmed a main source for the occurrence of plastics/microplastic. Although there are some reports that microplastics (MPs) can generate in leachate and refuse samples from the landfill, it exist many blanks for the evolution of physical and chemical characteristics of waste plastics and microplastics with different landfill age. To explore the process that large pieces of plastic are fractured into microplastics, the waste plastics with landfill age from 7 to 30 years are surveyed from a typical landfill in Shanghai. The results show that PE and PP are the most common types of landfilling plastics, and their chemical composition also have changed due to the creation of CO and –OH. Moreover, the crystallinity is affected by plastic type and landfill age. The crystallinity of PP increased from 24.9% to 56.8%, but for PE, the crystallinity decreased from 55.6% to 20.8%. The mechanical properties of waste plastics were reduced significantly, which may be caused by changes in carbon-chain molecules. Al, Ti, Co, and other metal elements were detected on the plastic surface. The hydrophobic behavior of waste plastic is constantly decreasing (102.2°–80.1°) under long-term landfilling. By investigating the changes in the physical and chemical characteristics of waste plastics with different landfill age can shed light upon the process of environmental weathering of waste plastics. This provide theoretical guidance for reducing the transport of microplastics to the environment.

Contaminated groundwater is considered as one of the most important pathways of human exposure to the geogenic contaminants. Present study has been conducted in a part of Indus basin to investigate the presence and spatial distribution of arsenic (As) and other trace metals in groundwater. The As concentration varies from bdl-255.6 μg/L and 24.6% of the 73 collected groundwater samples have As above world health organization (WHO) guideline of 10 μg/L. High concentration of As is found along the newer alluvium of Ravi River. As is found with high bicarbonate (HCO3−) and Iron (Fe) and low nitrate (NO3−) indicating reductive dissolution of Fe bearing minerals. However, silicate weathering along with high sulphate (SO42) and positive oxidation-reduction potential (ORP) indicates mixed redox conditions. Weathering of minerals along with other major hydrogeochemical process are responsible for composition of groundwater. With 31.5% of the samples, sodium bicarbonate (Na–HCO3) is the major water facies followed by magnesium bicarbonate (Mg–HCO3) in 30% of samples. As, Fe and other trace metals including copper (Cu), cadmium (Cd), chromium (Cr), zinc (Zn) were used to calculate the health risk for children and adults in the region. Out of 73 samples, 58% has high Fe, 32.8% has high Zn, and 4.1% has high Cd which are above the prescribed limits of WHO guidelines. Health risk of the population has been assessed using chronic dose index (CDI), hazardous quotients (HQ) and hazardous index (HI) for children and adults. The mean CDI values follows the order as Fe > Zn > Cu > As > Cr > Cd, while the HQ values indicates high As hazards for both children and adults. 43.8% of the groundwater samples have high HI for adults, however, 49.3% has high HI for children indicating higher risk for children compared to adults. A large-scale testing should be prioritized to test the wells for As and other trace metals in the study region to reduce health risks.

Following the 16TAN Husky oil spill along the North Saskatchewan River (NSR), the occurrence and natural attenuation of the petroleum hydrocarbons were assessed by analyzing the littoral zone sediments/oil debris collected from July 2016 to October 2017. Husky oil-free, mixed sediment-Husky oil, and Husky oil debris samples were identified for all the collected samples. Shoreline sediments were contaminated by mixed biogenic, pyrogenic and petrogenic inputs prior to the spill. Oil stranded on the shoreline of NSR was moved or buried due to the very dynamic conditions of the shoreline, or cleaned through a series of cleanup activities after the spill. Most normal alkanes were naturally weathered, whereas most of the branched alkanes and all of the saturated petroleum biomarkers remained. Some lighter molecular weight (e.g., 2 to 3-ring) polycyclic aromatic hydrocarbons (PAHs) were lost rapidly after the spill, whereas sulfur containing components, e.g., dibenzothiophenes and benzonaphthothiiophenes, and those having a heavier molecular weight did not change markedly even 15 months post-spill. Similarly, some light hydrocarbons (e.g., <C₁₀) were lost over the first kilometers from the point of entry (POE), while heavier hydrocarbons did not show any major differences away from the POE. Very large inter-site and inter-survey discrepancies were found for samples. Evaporation into the air and dissolution into water, combined with biodegradation, were together or independently the main contributors to the loss of the light molecular hydrocarbons.

Southwestern China contains the largest and most well-developed karst region in the world, and the potentially toxic elements (PTEs) content in the soils of the region is remarkably high. To explore the internal and external control factors and sources of soil PTEs enrichment in this area and to provide a basis for the treatment of PTE pollution, 113 soil samples were collected from Hengxian County, a karst region in Guangxi Province, southwestern China. The importance of eighteen influencing factors including parent material, weathering, physicochemical properties, topography and human activities were quantitatively analyzed by (partial) redundancy analysis. The sources of PTEs were identified using the Pb isotope ratio and absolute principal component score/multiple linear regression (APCS-MLR) model. The contents of all soil PTEs were higher than the corresponding background values of Guangxi soils. The contents in Cu, Zn, Cd, Hg and Pb were the highest in the soil from carbonate rock. The factor group of geological background and weathering explained 26.5% for the accumulation and distribution of soil PTEs and the influence of physicochemical properties was less than 2% but increased to 25.6% through interaction with weathering. Fe (47.1%), Al (42.1%), Mn (22%), chemical index of alteration (12.8%) and clay (11.9%) were the key factors affecting the soil PTEs, while the influence of human activities was weak. Pb isotope ratio and APCS-MLR classified 62.8–74% of soil PTEs as derived from natural sources, whereas 18.23% and 18.95% were derived from industrial activities and agricultural practice/traffic emissions, respectively. The Pb isotope ratio showed that the natural sources account for up to 90% of the Pb in the soil from carbonate rock, the highest contribution among the studied soils. The results of the study can provide background information on the soil PTEs contamination in the karst areas of China and other areas worldwide.

Trace elements and Hg isotopic composition were investigated in mineralized rocks, barren rocks, and mineral soils in the Xianfeng prospect, a shallow buried epithermal gold deposit in northeastern China, to understand whether this deposit has left a diagnostic geochemical fingerprint to its weathered horizon. All the rocks and soils display congruent patterns for immobile elements (large ion lithophile elements, high field strength elements, and rare earth elements), which reflect the subduction-related tectonic setting. Both mineralized rocks and soils showed common enrichment of elemental suite As–Ag–Sb–Hg, suggesting that the Xianfeng gold deposit has released these elements into its weathered horizon. Similar mercury isotopic composition was observed between mineralized rocks (δ²⁰²Hg: −0.21 ± 0.70‰; Δ¹⁹⁹Hg: −0.02 ± 0.12‰; 2SD) and barren rocks (δ²⁰²Hg: −0.46 ± 0.48‰; Δ¹⁹⁹Hg: 0.00 ± 0.10‰; 2SD), suggesting that mercury in the Xianfeng deposit is mainly derived from the magmatic rocks. Mineralized soils (δ²⁰²Hg: −0.44 ± 0.60‰; −0.03 ± 0.14‰; 2SD) and barren soils (δ²⁰²Hg: −0.54 ± 0.68‰; Δ¹⁹⁹Hg: −0.05 ± 0.14‰; 2SD) displayed congruent Hg isotopic signals to the underlying rocks, suggesting limited Hg isotope fractionation during the release of Hg from ore deposit to soils via weathering. This study reveals evidence of a simple and direct geochemical link between this shallow buried hydrothermal deposit and its weathered horizon, and highlights that the weathering of shallow-buried hydrothermal gold deposits can release a substantial amount of heavy metals (e.g. Hg, As and Sb) to surface soil.

Cadmium (Cd) contamination in soils has become a serious and widespread environmental problem, especially in areas with high natural background Cd values, but the mechanism of Cd enrichment in these areas is still unclear. This study uses the Guangxi Zhuang Autonomous Region (Guangxi), a typical area with a high background Cd level and Cd pollution related to mining activities, as an example to explore the source and predict areas with high Cd risk in soils based on the geographical detector method. The areas with high Cd in Guangxi soils were classified into non-mining areas and mining areas according to their potential Cd sources. The results show that the rich Cd content in the soils from the non-mining area of Guangxi was mainly derived from the soil type (q = 0.34), geological age (q = 0.27), rock type (q = 0.26) and geomorphic type (q = 0.20). Specifically, the Cd content was derived from the weathering and deposition processes of carbonatite from the Carboniferous system in the karst area. The high Cd content in the soils of the mining area of Guangxi was mainly derived from the area mined for mineral resources (q = 0.08) and rock type (q = 0.05). Specifically, the Cd content was derived from the mining of lead-zinc ores. The areas in Guangxi with a high risk of Cd soil pollution are mostly concentrated in karst areas, such as Hechi, Laibin, Chongzuo, southern Liuzhou and Baise, northern Nanning city and northeastern Guilin city, and some mining areas. These results indicated that the high Cd concentration in the soils of large areas of Guangxi is probably due to natural sources, while the high Cd concentration around mining areas is due to anthropogenic sources. The results will be useful for soil restoration and locating and controlling contaminated agricultural land.

Urban stormwater is a major source of chemical pollution to receiving waters. Anthropogenic materials in the built environment can be an important source of chemicals to stormwater runoff. Roofing materials can leach significant amounts of metals, which vary over the life of the roof. We report concentrations of three metals (As, Cu, Zn) leaching into runoff from experimental panels of 14 roofing materials over 4.5 years of weathering. Ten roofing materials leached metals. Several leached >10 ppb during one or more study periods. The most common correlate with metal concentration was panel age, followed by precipitation amount. Extrapolating from these observations, we estimated the loading of metals from each roofing material during the first 10 years following installation. Eight materials were predicted to leach metals above background at the end of the 10 years. In combination with information on the prevalence of different roofing materials in the Puget Sound region of the Pacific Northwest, we estimated the relative amount of metals contributed from roofing materials in this basin. Most arsenic and copper was estimated to be contributed by residential roofing; nearly all arsenic from wood shakes manufactured with copper chromated arsenic, and copper contributed mainly from treated wood shakes followed by copper granule-containing asphalt shingles. Most zinc was estimated to be contributed by commercial roofs, including Zincalume and painted metal roofs. Overall our data shows that roofing materials can be an important long-term source of As, Cu, and Zn to stormwater runoff. Compared with atmospheric deposition, roof materials were a significant source, particularly of As and Cu. To get a complete picture of metals sourced from buildings, there is a need to study whole roof systems, including gutters, downspouts, and HVAC systems, as well as metals contributed from homeowner-applied treatments to their roofs.