Systematic approach to source-sink apportionment of copper in paddy fields: Experimental observation, dynamic modeling and prevention strategy.

The accumulation of heavy metals in paddy rice severely impacts the health of consumers and plants. In this study, a systematic approach to source-sink apportionment of copper in paddy fields was developed by considering all bioenvironmental interfaces. Experimental data from two experimental fields (namely Field A and Field B) in the first harvest period was collected. Then, mass-balance-based models with dynamic critical loads were established to evaluate the year of excess for copper. The results indicated that irrigation water contributed the highest portion (96.2-98.8%) of total copper inputs. Under the business-as-usual scenario, the soil copper concentration of Field A and Field B might exceed the Taiwanese national standard within 66 and 24 years, respectively. In addition, alternate wet-dry irrigation was found to be one of the total solutions to reducing copper accumulation in soils by 17-48%. It could also provide a significant reduction of water usage in paddy fields by ~25%, thereby increasing the resilience to extreme climate change events. Lastly, based on the field observations, three improvement strategies on sustaining soil quality towards better agricultural environment were proposed. The connection of copper accumulation in soils with dietary and ecological risks was also briefly illustrated.

Wetland plant microbial fuel cells for remediation of hexavalent chromium contaminated soils and electricity production.

The plant microbial fuel cell (PMFC) is a novel technology which integrates plants, microbes, and electrochemical elements together to create renewable energy. However, information regarding using the PMFC system to remediate metal-contaminated soils is still limited. In this study, we evaluate the potential of PMFC systems to remediate soils polluted by Cr(VI). We compare different plants and different electrode materials with regard to their electricity generation and Cr(VI) removals under different soil Cr(VI) concentrations. In PMFC systems, the soil pH was transformed from slightly acidic to neutral, and the electrical conductivity was reduced during operation. The removal efficiency of Cr(VI) in soils could reach 99%, and the total Cr of soils could also be reduced. The closed circuit voltage of PMFC systems of Chinese pennisetum using the graphite carbon felt as the electrodes could reach the daily average value of 469.21 mV. PMFC systems have successfully demonstrated the ability to remove Cr(VI) from soils collected from actual metal-contaminated sites. Our results suggest that using PMFCs to remediate contaminated soils is promising, and the effects of decontamination are mostly contributed by bioelectrochemical processes and plant uptake.