Elimination kinetics of perfluorohexanoic acid in humans and comparison with mouse,rat and monkey

Major fluorinated chemical manufacturers have developed new short-chain per- and polyfluorinated substances with more favorable environmental, health and safety profiles. This study provides the first evaluation of the elimination half-life of perfluorohexanoic acid (PFHxA) from the blood of humans. PFHxA biomonitoring data were obtained from a recently published study of professional ski wax technicians. These data were analyzed to provide estimates of the apparent half-life of PFHxA from humans, and comparisons were made with kinetic studies of PFHxA elimination from mice, rats and monkeys. The apparent elimination half-life of PFHxA in highly exposed humans ranged between 14 and 49 d with a geomean of 32 d. The half-lives of PFHxA in mice, rats, monkeys and humans were proportional to body weight with no differences observed between genders, indicating similar volumes of distribution and similar elimination mechanisms among mammalian species. Compared to long-chain perfluoroalkyl acid analogs, PFHxA is rapidly cleared from biota. The consistent weight-normalized elimination half-lives for PFHxA in mammalian species indicates that results obtained from animal models are suitable for establishment of PFHxA benchmark dose and reference dose hazard endpoints for use in human risk assessments.     

除草剂氟磺胺草醚农田残留动态研究

为防止氟磺胺草醚污染农业生态环境，进行了该农药在土壤及花生，大豆上的残留动态试验研究。结果表明，氟磺胺草醚在土壤中的半衰期为１２－１８ｄ。生长后期，在植株及花生仁，大豆中均未检出残留，食用安全；提出了在这两种作物上合理使用氟磺胺草醚的准则建议。     

Effect of photo-biodegradation and biodegradation on the biogeochemical cycling of dissolved organic matter across diverse surface water bodies

The objective of this research was to quantify the temporal variation of dissolved organic matter(DOM) in five distinct waterbodies in watersheds with diverse types of land use and land cover in the presence and absence of sunlight. The water bodies were an agricultural pond, a lake in a forested watershed, a man-made reservoir, an estuary, and a bay. Two sets of samples were prepared by dispensing unfiltered samples into filtered samples in 1:10 ratio(V/V). The first set was exposed to sunlight(10 hr per day for 30 days) for examining the combined effect of photo-biodegradation, while the second set was stored in dark for examining biodegradation alone. Spectroscopic measurements in tandem with multivariate statistics were used to interpret DOM lability and composition. The results suggest that the agricultural pond behaved differently compared to other study locations during degradation experiments due to the presence of higher amount of microbial humic-like and protein-like components derived from microbial/anthropogenic sources. For all samples, a larger decrease in dissolved organic carbon(DOC) concentration(10.12% ±9.81% for photo-biodegradation and 6.65% ± 2.83% for biodegradation) and rapid transformation of DOM components(i.e., terrestrial humic-like components into microbial humic and protein-like components) were observed during photo-biodegradation experiments.Results suggest that sunlight facilitated DOM biodegradation, resulting in simpler recalcitrant molecules regardless of original composition. Overall, it was found that combined effects of light and bacteria are more efficient than bacterial effects alone in remineralizing and altering DOM, which highlights the crucial importance of sunlight in transforming aquatic DOM.     

Dissipation and residues of dimethyl disulfide in tomatoes and soil under greenhouse and open field conditions

Abstract

Tomatoes have been widely planted in greenhouses and fields in China. Soil-borne diseases are more harmful to tomatoes than other types of diseases. Dimethyl disulfide (DMDS) was used as a novel fumigant instead of methyl bromide to control soil-borne diseases. To assess the safety of DMDS for use on tomatoes, its dissipation and terminal residues were investigated at three different locations under greenhouse and open field conditions. The QuEChERS method was simplified using gas chromatography with mass spectrometry detection and combined with liquid-liquid extraction purification to allow determination of DMDS levels in both the tomatoes and the soil. The average recovery of the method was between 85.3 and 98.6%, with the relative standard deviation (RSD) ranging from to 1.9–10.3%. The dissipation and terminal residues of DMDS in the tomatoes and the soil were analyzed using the method, the results of which showed that the half-life of DMDS ranged from 0.3–6.5 d in the soil at three different locations. The terminal residues of DMDS in the tomatoes and the soil were not detected. This study provided data that the Chinese government can use to support appropriate and safe guidance for the use of DMDS on agriculture.     

Dissipation and metabolism of C-spiroxamine in soil under laboratory condition

Spiroxamine [SPX] belongs to a spiroketalamine group of substances. The biodegradation of [1,3-dioxolane-4-¹⁴C]-SPX has been examined in 2 soils of different physicochemical properties. The total recovery of radioactivity from soils was 98.6-103.5% of that applied. The total amount of extractable radioactivity declined with a simultaneous increase in non-extractable radioactivity. Volatile organics were detected at lower levels; however, mineralization played a marked effect on the route of SPX dissipation. The half-life ranges between 37 and 44 d. SPX does not undergo any enantioselective degradation. 4 metabolites: despropyl-SPX, desethyl-SPX, SPX N-oxide and SPX acid were identified, applying mass spectrometric technique. Sorption-desorption data fitted well with a Freundlich model in log form (r², 0.99). K_Dsorp ranged between 44 and 230, suggesting SPX ought to be considered as a substance with low leaching potential [groundwater ubiquity score (GUS), <1.8]. Furthermore, an overall low desorption of 1-11% indicates firm retention of SPX by the soils.     

Half-lives of serum PCB congener concentrations in environmentally exposed early adolescents

The aim was to determine half-life of six most abundant PCB congeners in the body of early adolescents. In 304 environmentally exposed children, PCB serum concentration was determined at the age of 8 and 12 years. Half-life was determined for each child assuming exponential decrease or for the whole cohort using multiple regression. Results obtained by both approaches were in agreement. PCB reuptakes corrupting half-life estimates for each child and each congener were evaluated. If one of the serum PCB concentration values fell below the level of detection (LOD) the pair was excluded and if PCB half-life value exceeded the arbitrary value of 30 years. The following median half-lives in years 4.46, 10.59, 9.7, 4.7, 9.1 and 9.8 were obtained for PCB congeners 118, 138⁺¹⁶³, 153, 156⁺¹⁷¹, 170 and 180, respectively. The elimination half-life values were not systematically related to PCB serum concentration at any examination age. Between half-life values, percentage of children with significant reuptakes and PCB congener abundance in serum were found significant associations.     

Quantitative analysis of acetamiprid and imidacloprid residues in tomato fruits under greenhouse conditions

Abstract

A selective liquid chromatographic analytical method was studied for determination of two neonicotinoids, acetamiprid and imidacloprid, in tomato fruits under greenhouse conditions in Egypt. The fruits were extracted and cleaned up by QuEChERS method followed by HPLC determination. The method showed a good linearity with a determination coefficient (R²) of higher than 0.99 for the 0.0125–0.15 µg/mL concentration range. The method was validated using a blank tomato spiked at 5, 25 and 50 mg/kg and the recovery percentages were 83.71, 94.52 and 97.49% for acetamiprid and 88.59, 89.63 and 90.18% for imidacloprid, respectively. The rates of dissipation of both pesticides were studied and the preharvest intervals (PHIs) were calculated. Imidacloprid dissipated faster than acetamiprid and half-life periods were 1.30 and 2.07 days, respectively. Acetamiprid and imidacloprid residues were below the already established European maximum residue limits (EU MRLs) (0.5 mg/kg) 3 and 5 days after application, respectively.     

Persistence of C-labeled atrazine and its residues in a field lysimeter soil after 22 years

Twenty-two years after the last application of ring-¹⁴C-labeled atrazine at customary rate (1.7 kg ha⁻¹) on an agriculturally used outdoor lysimeter, atrazine is still detectable by means of accelerated solvent extraction and LC-MS/MS analysis. Extractions of the 0-10 cm soil layer yielded 60% of the residual ¹⁴C-activity. The extracts contained atrazine (1.0 μg kg⁻¹) and 2-hydroxy-atrazine (42.5 μg kg⁻¹). Extractions of the material of the lowest layer 55-60 cm consisting of fine gravel yielded 93% of residual ¹⁴C-activity, of which 3.4 μg kg⁻¹ was detected as atrazine and 17.7 μg kg⁻¹ was 2-hydroxy-atrazine. The detection of atrazine in the lowest layer was of almost four times higher mass than in the upper soil layer. These findings highlight the fact that atrazine is unexpectedly persistent in soil. The overall persistence of atrazine in the environment might represent a potential risk for successive groundwater contamination by leaching even after 22 years of environmental exposure.     

4种农药在稻田水中的残留降解

对乐果、杀虫单、丁草胺和氰戊菊酯４种 经，在稻田水中的残留降解情况，进行了及比较。结果表明，４种农药在稻田水中的残留降解符合Ｃ－Ｃｏ．３＾ｋｔ或Ｃ＝Ａ．ｅ＾－１６＋Ｂ．３＾βｉ的数学式，据此可计算其平均降解半衰期（ｔ０．５）分别为：１．８６、１．３５、０．８８和０．３８ｄ，其中丁草胺和氰戊菊酯的降解前快后慢，氰戊菊酯的降解愉丁乐果，土壤吸附氰戊菊酯是其降解快的重要原因，脂溶性农药对水环境的污染要轻     

Dissipation of Phosalone and Diazinon in Fresh and Dried Alfalfa

The objectives of this study were to determine the persistence of phosalone (S-6-chloro-2,3-dihydro-2-oxobenzoxazol-3-ylmethyl O, O-diethyl phosphorodithioate) and diazinon (O,O-diethyl O-2-isopropyl-6-methylpyrimidin-4-yl phosphorothioate) residues in fresh and baled alfalfa under field conditions. Plots of alfalfa were sprayed with each insecticide. Fresh alfalfa was sampled up to 20 days after treatment, and dried alfalfa was sampled up to 25 weeks after baling. Samples were analyzed for residues using high performance liquid chromatography (HPLC) equipped with a UV detector. The half-lives of diazinon and phosalone in fresh alfalfa were 1.8 and 3.3 days, respectively. In baled alfalfa the half-life of diazinon and phosalone were 2.8 and 16.7 weeks, respectively. No diazinon residues were detected in baled alfalfa, sampled after week 9, although the concentration of phosalone found at week 25 was 5.51 mg/kg.