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Science of The Total Environment
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Item-typ:Veröffentlichung, Sulfidation of sea urchin-like zinc oxide nanospheres: Kinetics, mechanisms, and impacts on growth of Escherichia coliNanoscale zinc oxide (n-ZnO) with different morphology and sizes has been used in personal care products due to their antibacterial properties, resulting in discharge of n-ZnO into the environment with potential toxic effect to ecological systems. Sulfidation is one of pathways of transformation of n-ZnO, but a very limited information on the conversion of n-ZnO under sulfidic environment with special morphology such as sea urchin-like zinc oxide nanospheres (ZnO-NSs) is available to know the potential environmental risks of n-ZnO. Herein, sea urchin-like ZnO-NSs with an average size of 78 nm were synthesized and adopted as the model n-ZnO of special morphology. The ZnO-NPs at average sizes of 71 nm (ZnO-NPs-71), 48 nm (ZnO-NPs-48), and 17 nm (ZnO-NPs-17) nm were used to examine possible differences in the sulfidation between the sea urchin-like ZnO-NSs and ZnO-NPs. A new analytical method selectively dissolving ZnO over ZnS in partially sulfidized n-ZnO was developed and applied to understand the kinetics of n-ZnO sulfidation. The sulfidation rate constant (ks) of sea urchin-like ZnO-NSs was 2.9 × 10−3 h−1, comparable to that of ZnO-NPs-71 (4.1 × 10−3 h−1), but much lower than those of ZnO-NPs-48 (20.1 × 10−3 h−1) and ZnO-NPs-17 (67.8 × 10−3 h−1). This might be attributed to the differences in the specific surface area; ks positively correlated with the specific surface area (R2 = 0.97). Natural organic matter (NOM) decreased dissolution and sulfidation of the sea urchin-like ZnO-NSs. Aggregate ZnS nanocrystals instead of the original sea urchin-like ZnO-NSs were observed. We proposed that sea urchin-like ZnO-NSs were transformed to ZnS through a dissolution-precipitation pathway, consistent with the sulfidation pathway of ZnO-NPs. Sulfidation drastically reduced toxicity of sea urchin-like ZnO-NSs to Escherichia coli due to negligible dissolution of ZnS nanocrystals. These results greatly improved our understanding of the transformation and potential risks of n-ZnO with special morphology.Wissenschaftlicher ArtikelBand:74126 30 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Cadmium in groundwater − A synopsis based on a large hydrogeochemical data setElevated cadmium (Cd) concentrations in groundwater have widespread implications for water supply and agriculture. The aqueous chemistry of Cd is considered not complex; however, aside from intense industrial pollution, multi-faceted hydrogeochemical interactions control Cd mobility. Therefore, the behavior of Cd in groundwater was investigated through statistical analyses of a large hydrogeochemical data set, which contained analyses from 6300 sampling locations in Northern Germany. Cadmium concentrations of above 0.5 μg/L were linked to groundwater conditions caused (1) by woodlands in connection with acidification or (2) elevated nitrate concentrations beneath farmland due to fertilization. Comparably, both geogenic and anthropogenic Cd input were less important. The main hydrogeochemical parameters affecting Cd mobility were pH and redox potential, which are probably linked to Cd sorption to mineral surfaces and Cd release from carbonates and sulfides, such as pyrite. Thus, Cd concentrations were primarily elevated when groundwater conditions were oxic and autotrophic nitrate reducing. In addition, enhanced groundwater recharge and limited Cd retention capacity by the aquifer matrix were responsible for elevated Cd concentrations in groundwater, potentially breaching legal regulations.Wissenschaftlicher ArtikelBand:68988 105 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Generating false negatives and false positives for As and Mo concentrations in groundwater due to well installationGroundwater monitoring relies on the acquisition of ‘representative’ groundwater samples, which should reflect the ambient water quality at a given location. However, drilling of a monitoring well for sample acquisition has the potential to perturb groundwater conditions to a point that may prove to be detrimental to the monitoring objective. Following installation of 20 monitoring wells in close geographic proximity in central Florida, opposing concentration trends for As and Mo were observed. In the first year after well installation As and Mo concentrations increased in some wells by a factor of 2, while in others As and Mo concentrations decreased by a factor of up to 100. Given this relatively short period of time, a natural change in groundwater composition of such magnitude is not expected, leaving well installation itself as the likely cause for the observed concentration changes. Hence, initial concentrations were identified as ‘false negatives’ if concentrations increased with time or as ‘false positives’ if concentrations decreased. False negatives were observed if concentrations were already high, i.e., the As or Mo were present at the time of drilling. False positives were observed if concentrations were relatively lower, i.e., As or Mo were present at low concentrations of approximately 1 to 2 μg/L before drilling, but then released from the aquifer matrix as a result of drilling. Generally, As and Mo were present in the aquifer matrix in either pyrite or organic matter, both of which are susceptible to dissolution if redox conditions change due to the addition of oxygen. Thus, introduction of an oxidant into an anoxic aquifer through use of an oxygen saturated drilling fluid served as the conceptual model for the trends where concentrations decreased with time. Mixing between drilling fluid and groundwater (i.e., dilution) was used as the conceptual model for scenarios where increasing trends were observed. Conceptual models were successfully tested through formulation and application of data-driven reactive transport models, using the USGS code MODFLOW in conjunction with the reactive multicomponent transport code PHT3D.Wissenschaftlicher ArtikelBand:631-63277 70 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Arsenic abundance and variation in golf course lakesMonosodium methanearsonate (MSMA) is a commonly used herbicide on golf courses. To investigate the variation in abundance of arsenic (As) after MSMA application, 28 golf course lakes were monitored monthly for one year. The As concentrations varied substantially in and between individual lakes with values up to 124 μg/L (mean = 10.9 μg/L, n = 336). This is considerably higher than the As concentrations in comparable “non-golf course” lakes (up to 100-times) in the study area. The highest values of As in the lakes were generally observed in the late spring and early summer and corresponded to the intensity of MSMA applications. Arsenic seems to be sequestered by the golf course lake sediments with concentrations as high as 302 mg/kg, which were significantly higher than the 0.1 to 3 mg/kg expected for comparable sediments in central Florida. Arsenic correlates well with Fe in the top 15 cm of the lake sediments suggesting that As is sorbed by hydrous ferric oxides (HFO). As long as conditions are in favour of HFO stability, As is retained in the lake sediments preventing its migration into the Floridan aquifer systems. However, once the loading capacity of the sediment is reached or when as a result of changing physico-chemical conditions HFO may become unstable, As may enter the Floridan aquifer.Wissenschaftlicher ArtikelBand:394Heft:2-359 53