A laboratory incubation study was conducted to determine the effect of drinking-water treatment residuals (WTRs) on arsenic (As) bioaccessibility and phytoavailability in a poorly As-sorbing soil contaminated with arsenical pesticides and fertilized with triple super phosphate (TSP). The Immokalee soil (a sandy spodosol with minimal As-retention capacity) was amended with 2 WTRs (Al and Fe) at 5 application rates ranging between 0% and 5% wt/wt. Sodium arsenate and TSP were used to spike the soil with 90 mg As kg(-1) and 115 mg P kg(-1), respectively. Bioaccessible As was determined at time 0 (immediately after spiking), and at 6 and 12 months of equilibration using an in vitro gastrointestinal test, and As phytoavailability was measured with a 1-M KC1 extraction test. Arsenic phytoavailability decreased immediately after spiking (20% availability at 5% rate), but only after 6 months for the Al-WTR- and the Fe-WTR-amended soil, respectively. Arsenic bioaccessibility simulated for the stomach and intestine phases showed that the Fe-WTR was more effective than the Al-WTR in resisting the harsh acidic conditions of the human stomach, thus preventing As release. Both the phytoavailable As and the bioaccessible As were significantly correlated (p < 0.001) for soil spiked with either Al- or Fe-WTR. Both WTRs were able to decrease soil As bioaccessibility irrespective of the presence or absence of P, which was added as TSP. Results indicate the potential of WTRs in immobilizing As in contaminated soils fertilized with P, thereby minimizing soil As bioaccessibility and phytoavailability.
A constructed wetland is a wastewater treatment facility that duplicates the processes in natural wetlands. Constructed wetlands are complex, integrated systems in which water, plants, animals, microorganisms, and the environment interact to improve water quality. Phytoremediation, defined as cleansing of the environment using vegetation, is the primary water treatment process in constructed wetlands. The advantages of phytoremediation using constructed wetlands are that it is environmentally friendly, a sustainable technology, and cost‐effective; the primary disadvantages are potentially incomplete removal of pollutants and pest attraction. Successful implementation of phytoremediation technology in constructed wetlands is a function of a number of interrelated biophysicochemical factors, including the types and fate of toxicants, characteristics of soil and sediment, plant species and plant uptake, hydrology and water flow, and microbial population. Hence, phytoremediation by constructed wetlands generally reflects an integrated multidisciplinary effort that combines plant biology, microbiology, surface chemistry, hydrology, and environmental engineering. The initial construction of wetlands, taking into account all these factors to design the most appropriate and effective method for removing target pollutants is labor‐intensive and expensive, but low maintenance and operating costs make constructed wetlands a much more economically viable alternative to conventional physical and chemical treatments. Above all, the use of plants in environmental cleanup may guarantee a greener and cleaner planet for us and for future generations.
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