During the last decades, high population growth and exportoriented economics in Vietnam have led to a tremendous intensifi cation of rice production, which in turn has signifi cantly increased the amount of pesticides applied in rice cropping systems. Since pesticides are toxic by design, there is a natural concern on the impact of their presence in the environment on human health and environmental quality. Th e present study was designed to examine the water regime and fate of pesticides (fenitrothion, dimethoate) during two consecutive rice crop seasons in combined paddy rice-fi sh pond farming systems in northern Vietnam. Major results revealed that 5 and 41% (dimethoate), and 1 and 17% (fenitrothion) of the applied mass of pesticides were lost from the paddy fi eld to the adjacent fi sh pond during spring and summer crop seasons, respectively. Th e decrease of pesticide concentration in paddy surface water was very rapid with dissipation half-life values of 0.3 to 0.8 and 0.2 d for dimethoate and fenitrothion, respectively. Key factors controlling the transport of pesticides were water solubility and paddy water management parameters, such as hydraulic residence time and water holding period. Risk assessment indicates that the exposure to toxic levels of pesticides for aquaculture (Cyprinus carpio, Daphnia magna) is signifi cant, at least shortly after pesticide application.
In the present study, persistence and leaching of dimethoate and fenitrothion in a paddy soil were studied under the typical conditions of northern Vietnam. The experiments were conducted on a sandy loam soil (pH 8.1) planted with a local rice variety (Oryza sativa L. var. Nep87) during two consecutive cropping seasons. Concentrations of dimethoate and fenitrothion were monitored in paddy topsoil (5 cm) and in soil water in 20 and 40 cm soil depths. Maximum concentrations were detected in topsoil on day 1 after treatment (DAT 1) or DAT 2 and corresponded to 29-30% (dimethoate) and 2-3% (fenitrothion) of applied mass. Dissipation of both pesticides from topsoil showed strong bi-phasic behavior. Despite differences in their properties and seasonal conditions, calculated dissipation half-lives were always less than one day, indicating strong influence of transport processes. The transport within soil was very rapid: Already 6 h after application dimethoate and fenitrothion were found at soil depths of 20 and 40 cm, suggesting preferential transport acting under submerged conditions. It points to high groundwater vulnerability during pesticide application season on paddy rice in the studied area. To protect groundwater, actions are required both in agricultural and legal fields: Current pesticide application practices should be revised together with a more stringent authorization procedure, market regulation, and an introduction of pesticide groundwater thresholds.
Water hyacinth is a substantial and quick‐growing plant that can strongly invade and negatively affect the aquatic ecosystem, causing many problems to the water environment by consuming nutrients and oxygen from surface water. However, the hierarchical porous carbon derived from water hyacinth can be employed for the removal of oil spills, heavy metals, or wastewater nutrients. Recently, water‐hyacinth‐derived carbon aerogel has been utilized as electrode for the desalination of brackish water using membrane capacitive deionization (MCDI) technology. In this research, lignocellulose aerogels were synthesized from water hyacinth, which were then pyrolyzed to obtain carbon aerogel and then treated with KOH to acquire activated carbon aerogel, with the corresponding surface area of 51 and 100 m2 g−1. The desalination capacity of the MCDI device was also evaluated using a 200 ppm NaCl feed water solution with an applied potential of 1.2 V. A high salt adsorption capacity value of 14.69 mg g−1 was achieved after 3000 s. These results will lead a new research area of biomass and bio‐waste conversion to fabricate CDI‐utilized carbon aerogel electrodes.
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