The residual levels and dissipation rate of trichlorfon, and its degradation product, dichlorvos, in cabbage crops and the soil in which these were grown, were determined by gas chromatography at two geographically distant experimental sites, one in Kunming and one in Beijing, China. Trichlorfon was applied at two dosages (900 g ai ha−1 and 1350 g ai ha−1). Maximum final residues of trichlorfon in soil and cabbage were 1.23 mg kg−1 and 1.81 mg kg−1 respectively at Kunming, and 0.35 mg kg−1 and 0.70 mg kg−1 respectively at Beijing. However, the final residues of dichlorvos in both cabbage and soil was only 0.04 mg kg−1 at Kunming, and only 0.03 mg kg−1, or “not detectable”, at Beijing. The mean half-life of trichlorfon in cabbage was 1.80 d with a dissipation rate of 90% over 5 d, while that in soil was 3.05 d with a dissipation rate of 90% over 14 d at one experimental site. The dissipation rates of trichlorfon and its degradation product dichlorvos at the two experimental sites were different, suggesting that degradation of these pesticides was affected by local soil characteristics and climate. When applied at both the recommended dosage and at 1.5 times this, no detectable residues of either trichlorfon or dichlorvos were found in soil or cabbage at harvest. Although trichlorfon can easily degrade into dichlorvos, which is highly toxic to humans and other animals, the observed low residual levels of dichlorvos suggest that trichlorfon is safe when applied at the recommended dosage. 相似文献
Polyaniline doped with SO(4)(2-)/TiO(2) superacid shows good conductive ability. When used in a strippable coating film for decontaminating radioactive pollutants, the SO(4)(2-)/TiO(2) solid superacid replacing HCl exhibits higher electrical conductivity (7.01 s/cm) and a decontamination ratio higher than 97%. Coating and electrolyzing the film in solution or in dry medium were effective methods, the latter was more promising for decontaminating radioactive pollutants which were attached to the surface or within the body of equipments used in nuclear industry. 相似文献
Human health risks associated with the consumption of metal-contaminated fish over extended periods have become a concern particularly in Taiwan, where fish is consumed on a large scale. This study applied the interaction-based hazard index (HI) to assess the mixture health risks for fishers and non-fishers who consume the arsenic (As), copper (Cu), and zinc (Zn) contaminated milkfish from As-contaminated coastal areas in Taiwan, taking into account joint toxic actions and potential toxic interactions. We showed that the interactions of As–Zn and Cu–Zn were antagonistic, whereas As–Cu interaction was additive. We found that HI estimates without interactions considered were 1.3–1.6 times higher than interactive HIs. Probability distributions of HI estimates for non-fishers were less than 1, whereas all 97.5%-tile HI estimates for fishers were >1. Analytical results revealed that the level of inorganic As in milkfish was the main contributor to HIs, indicating a health risk posed to consumers of fish farmed in As-contaminated areas. However, we found that Zn supplementation could significantly decrease As-induced risk of hematological effect by activating a Zn-dependent enzyme. In order to improve the accuracy of health risk due to exposure to multiple metals, further toxicological data, regular environmental monitoring, dietary survey, and refinement approaches for interactive risk assessment are warranted. 相似文献
To evaluate the effects of crude oil water accommodated fraction (WAF) on marine phytoplankton community, natural phytoplankton collected seasonally from the Yueqing bay were exposed to eight groups of crude oil WAF for 15 days under laboratory conditions. Chlorophyll a and cell density were measured, and species of phytoplankton were identified every 24 h to reflect the change of phytoplankton community. The results showed that (1) High concentrations (??2.28 mg l???1) of oil pollution would greatly restrain phytoplankton growth (p?< 0.001), decrease chlorophyll a content and cell density, whereas low concentrations (??1.21 mg l???1) did not restrain its growth but rather promoted the phytoplankton growth. (2) The biodiversity, evenness, and species number of phytoplankton were all significantly influenced by crude oil WAF in all seasons (p?<?0.001). (3) The dominant species changes were different under different pollutant concentrations in different seasons. Different species had different tolerances to the oil pollution, thus leading to abnormal succession. 相似文献
The Wells-Riley model invokes human physiological and engineering parameters to successfully treat airborne transmission of infectious diseases. Applications of this model would have high potentiality on evaluating policy actions and interventions intended to improve public safety efforts on preventing the spread of COVID-19 in an enclosed space. Here, we constructed the interaction relationships among basic reproduction number (R0) − exposure time − indoor population number by using the Wells-Riley model to provide a robust means to assist in planning containment efforts. We quantified SARS-CoV-2 changes in a case study of two Wuhan (Fangcang and Renmin) hospitals. We conducted similar approach to develop control measures in various hospital functional units by taking all accountable factors. We showed that inhalation rates of individuals proved crucial for influencing the transmissibility of SARS-CoV-2, followed by air supply rate and exposure time. We suggest a minimum air change per hour (ACH) of 7 h−1 would be at least appropriate with current room volume requirements in healthcare buildings when indoor population number is < 10 and exposure time is < 1 h with one infector and low activity levels being considered. However, higher ACH (> 16 h−1) with optimal arranged-exposure time/people and high-efficiency air filters would be suggested if more infectors or higher activity levels are presented. Our models lay out a practical metric for evaluating the efficacy of control measures on COVID-19 infection in built environments. Our case studies further indicate that the Wells-Riley model provides a predictive and mechanistic basis for empirical COVID-19 impact reduction planning and gives a framework to treat highly transmissible but mechanically heterogeneous airborne SARS-CoV-2.
• NOM formed more C-DBPs while amino acids formed more N-DBPs during chlorination• Aspartic acid and asparagine showed the highest toxicity index during chlorination• Dichloroacetonitrile might be a driving DBP for cytotoxicity and genotoxicity• Dichloroacetonitrile dominated the toxicity under different chlorination conditions Chlorination, the most widely used disinfection process for water treatment, is unfortunately always accompanied with the formation of hazardous disinfection byproducts (DBPs). Various organic matter species, like natural organic matter (NOM) and amino acids, can serve as precursors of DBPs during chlorination but it is not clear what types of organic matter have higher potential risks. Although regulation of DBPs such as trihalomethanes has received much attention, further investigation of the DBPs driving toxicity is required. This study aimed to identify the important precursors of chlorination by measuring DBP formation from NOM and amino acids, and to determine the main DBPs driving toxicity using a theoretical toxicity evaluation of contributions to the cytotoxicity index (CTI) and genotoxicity index (GTI). The results showed that NOM mainly formed carbonaceous DBPs (C-DBPs), such as trichloromethane, while amino acids mainly formed nitrogenous DBPs (N-DBPs), such as dichloroacetonitrile (DCAN). Among the DBPs, DCAN had the largest contribution to the toxicity index and might be the main driver of toxicity. Among the precursors, aspartic acid and asparagine gave the highest DCAN concentration (200 g/L) and the highest CTI and GTI. Therefore, aspartic acid and asparagine are important precursors for toxicity and their concentrations should be reduced as much as possible before chlorination to minimize the formation of DBPs. During chlorination of NOM, tryptophan, and asparagine solutions with different chlorine doses and reaction times, changes in the CTI and GTI were consistent with changes in the DCAN concentration. 相似文献