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91.
This study attempted to investigate whether increased hair lead concentrations due to environmental exposure are accompanied by parallel increases in blood lead concentrations. A sample set consisting of both occupationally-exposed individuals and persons from the general population was investigated. The lead content of scalp and pubic hair from the general population (n=189), traffic police personnel (n=27) and battery workers (n=22) were analysed. The hair samples were taken from the nape of the neck by cutting 23 cm closest to the scalp and cleaned using a washing procedure developed in our laboratory. The effectiveness of the washing procedure was partly determined by examining the scanning electron micrographs of the hair samples. Venous samples of blood were taken from each volunteer's arm.The traffic police and battery plant operators sampled had significantly higher average scalp hair and pubic hair lead levels than the non occupationally-exposed general population. No significant differences were found between the blood lead values of these workers and the general population. Compared to the general population both occupationally-exposed groups had significantly more symptoms of lead toxicity.Lead particles were still observed on the hair shafts after the washing procedure. The amount of such lead contamination was difficult to quantify, the problem being further exacerbated by the difference in hair texture of the persons sampled. This exogenous contamination therefore detracts from the usefulness of hair as an indicator of lead exposure. 相似文献
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93.
The identification of characteristics of noise-susceptible (S) or noise-resistant (R) individuals is necessary for the development of noise-susceptibility risk profiles. Fifty-six naval aviators, categorized as having either incurred a hearing loss, i.e., hearing threshold levels (HTLs) > 40 dB at 4–8 kHz or retained normal hearing, i.e., HTLs ≤ 25 dB at 125 Hz-8 kHz, after thousands of flight hours were compared along several auditory and non-auditory dimensions. A number of variables occurred differentially in the two groups: Minimal Auditory Intensity Differential (MAID) scores at 2 kHz (p < 0.01) and 4 kHz (p < 0.001); iris pigmentation (blue eyes were over-represented in the S group; p < 0.05); systolic blood pressure (sitting; S group was higher; p < 0.05); calcium, albumin, and LDH levels (higher in the R group; p < 0.05); and present tobacco usage (more S aviators were currently smokers; p < 0.05). The S population also tended (p < 0.10) to exhibit elevated cholesterol and triglyceride levels as well as higher contralateral acoustic reflexes, and to have fewer individuals who had never smoked. Although no classic profile of the S or R individual definitely emerged, results suggested that at least one measurement device (MAID test) may serve as an “early warning” of imminent noise-induced damage. Further research, however, is required to test this possibility. 相似文献
94.
A maize (Zea mays L.) hybrid was infested with 30 southwestern corn borer [Diatraea grandiosella (Dyar)] larvae per plant at 4, 5, 6, 7 or 8 weeks after planting in a three-year study conducted at Mississippi State, Mississippi. Visual ratings of leaf feeding damage were highest when plants were infested 5 weeks after planting. Plant height increased linearly with the age of plants at infestation. Height of infested plants was significantly less than uninfested plants only when infestations were made 4 weeks after planting. The relationship between age of plants at infestation and yield was curvilinear. Yields were significantly reduced at all infestation times; however, the least yield reduction occurred when plants were infested 6 weeks after planting. To evaluate resistance to southwestern corn borer damage, infestation at 4 or 5 weeks after planting appeared to be most satisfactory. Yield reductions following infestation at 7 and 8 weeks after planting indicated that, when infestations are late, leaf feeding damage ratings alone may not be satisfactory indicators of plant damage. 相似文献
95.
The crab Pachygrapsus laevimanus and the zebra winkle Austrocochlea constricta were exposed for 40 d to uranium (1.5 to 10 mg l-1) in continuous-flow sea water in separate starved and fed treatments, and the kinetics of uranium bioaccumulation were estimated from an exponential model. Starved and fed crabs took up U at a similar rate, which suggests that sea water was the major source of U to the crab; the fed crabs excreted U more rapidly than the starved crabs and this led to a lower net uptake of U by fed crabs. Fed and starved winkles took up U at similar rates and excreted it at similar rates, so the sea water was also the major source of U to winkles. Crabs took up more U than winkles; the concentration factors were 7 to 18 and 4, respectively. Uranium turnover was quite slow for both species (11 to 36 d) as it was also for winkle shells (6 d); this suggests that the rate-limiting processes which control turnover are biological (e.g. growth or tissue replacement) or physical (e.g. diffusion into the shell) rather than chemical (e.g. precipitation, adsorption or exchange). There was no effect of increasing U concentration in water on the U kinetic parameters. 相似文献
96.
Nitrite occurs naturally in fresh waters as a result of nitrification of ammonia and denitrification of nitrate, and its concentration can be enhanced by partial oxidation of ammoniacal discharges. Nitrite is toxic to vertebrates including fish and a principal effect is the conversion of haemoglobin to methaemoglobin which is incapable of oxygen transport although there are circulatory and tissue effects as well. The toxic species is the nitrite ion (NO2) which is believed to enter the blood via the branchial chloride/bicarbonate exchange and fish such as salmonids with high chloride uptake rates are more susceptible than those with low chloride uptake rates, for example carp. Nitrite toxicity is strongly aleviated by chloride and the concentration ratio of these ions is of great importance in assessing toxicity. Short term and long term toxicity data for a variety of fish species are presented. There are no field data on fish populations in waters where nitrite was the only pollutant. However extensive field surveys indicated that, waters with a mean chloride concentration of 25 mg l-1 in good salmon fisheries were associated with concentrations of nitrite below 50 μg l-1 N · NO2, good coarse fisheries below 100 μg l-1 N · NO2. 相似文献
97.
98.
Objectives: Engaging in active transport modes (especially walking) is a healthy and environmentally friendly alternative to driving and may be particularly beneficial for older adults. However, older adults are a vulnerable group: they are at higher risk of injury compared with younger adults, mainly due to frailty and may be at increased risk of collision due to the effects of age on sensory, cognitive, and motor abilities. Moreover, our population is aging, and there is a trend for the current cohort of older adults to maintain mobility later in life compared with previous cohorts. Though these trends have serious implications for transport policy and safety, little is known about the contributing factors and injury outcomes of pedestrian collision. Further, previous research generally considers the older population as a homogeneous group and rarely considers the increased risks associated with continued ageing.Method: Collision characteristics and injury outcomes for 2 subgroups of older pedestrians (65–74 years and 75+ years) were examined by extracting data from the state police–reported crash dataset and hospital admission/emergency department presentation data over the 10-year period between 2003 and 2012. Variables identified for analysis included pedestrian characteristics (age, gender, activity, etc.), crash location and type, injury characteristics and severity, and duration of hospital stay. A spatial analysis of crash locations was also undertaken to identify collision clusters and the contribution of environmental features on collision and injury risk.Results: Adults over 65 years were involved in 21% of all pedestrian collisions. A high fatality rate was found among older adults, particularly for those aged 75 years and older: this group had 3.2 deaths per 100,000 population, compared to a rate of 1.3 for 65- to 74-year-olds and 0.7 for adults below 65 years of age. Older pedestrian injuries were most likely to occur while crossing the carriageway; they were also more likely to be injured in parking lots, at driveway intersections, and on sidewalks compared to younger cohorts. Spatial analyses revealed older pedestrian crash clusters on arterial roads in urban shopping precincts. Significantly higher rates of hospital admissions were found for pedestrians over the age of 75 years and for abdominal, head, and neck injuries; conversely, older adults were underrepresented in emergency department presentations (mainly lower and upper extremity injuries), suggesting an increased severity associated with older pedestrian injuries. Average length of hospital stay also increased with increasing age.Conclusion: This analysis revealed age differences in collision risk and injury outcomes among older adults and that aggregate analysis of older pedestrians can distort the significance of risk factors associated with older pedestrian injuries. These findings have implications that extend to the development of engineering, behavioral, and enforcement countermeasures to address the problems faced by the oldest pedestrians and reduce collision risk and improve injury outcomes. 相似文献
99.
Influence of Riparian Seepage Zones on Nitrate Variability in Two Agricultural Headwater Streams 下载免费PDF全文
Mark R. Williams Anthony R. Buda Herschel A. Elliott Kamini Singha James Hamlett 《Journal of the American Water Resources Association》2015,51(4):883-897
Riparian seeps have been recognized for their contributions to stream flow in headwater catchments, but there is limited data on how seeps affect stream water quality. The objective of this study was to examine the effect of seeps on the variability of stream NO3‐N concentrations in FD36 and RS, two agricultural catchments in Pennsylvania. Stream samples were collected at 10‐m intervals over reaches of 550 (FD36) and 490 m (RS) on 21 occasions between April 2009 and January 2012. Semi‐variogram analysis was used to quantify longitudinal patterns in stream NO3‐N concentration. Seep water was collected at 14 sites in FD36 and 7 in RS, but the number of flowing seeps depended on antecedent conditions. Seep NO3‐N concentrations were variable (0.1‐29.5 mg/l) and were often greater downslope of cropped fields compared to other land uses. During base flow, longitudinal variability in stream NO3‐N concentrations increased as the number of flowing seeps increased. The influence of seeps on the variability of stream NO3‐N concentrations was less during storm flow compared to the variability of base flow NO3‐N concentrations. However, 24 h after a storm in FD36, an increase in the number of flowing seeps and decreasing streamflow resulted in the greatest longitudinal variability in stream NO3‐N concentrations recorded. Results indicate seeps are important areas of NO3‐N delivery to streams where targeted adoption of mitigation measures may substantially improve stream water quality. 相似文献
100.
Development of the Spatial Rainfall Generator (SRGEN) for the Agricultural Policy/Environmental Extender Model 下载免费PDF全文
Jaehak Jeong Jimmy R. Williams Colleen G. Rossi Robin A. Taylor Xiuying Wang William E. Fox 《Journal of the American Water Resources Association》2015,51(1):154-167
Accurate spatial representation of climatic patterns is often a challenge in modeling biophysical processes at the watershed scale, especially where the representation of a spatial gradient in rainfall is not sufficiently captured by the number of weather stations. The spatial rainfall generator (SRGEN) is developed as an extension of the “weather generator” (WXGEN), a component of the Agricultural Policy/Environmental eXtender (APEX) model. SRGEN generates spatially distributed daily rainfall using monthly weather statistics available at multiple locations in a watershed. The spatial rainfall generator as incorporated in APEX is tested on the Cowhouse watershed (1,178 km2) in central Texas. The watershed presented a significant spatial rainfall gradient of 2.9 mm/km in the lateral (north‐south) directions based on four rainfall gages. A comparative analysis between SRGEN and WXGEN indicates that SRGEN performs well (PBIAS = 2.40%). Good results were obtained from APEX for streamflow (NSE = 0.99, PBIAS = 8.34%) and NO3‐N and soluble P loads (PBIAS ≈ 6.00% for each, respectively). However, APEX underpredicted sediment yield and organic N and P loads (PBIAS: 24.75‐27.90%) with SRGEN, although its uncertainty in output was lower than WXGEN results (PBIAS: ?13.02 to ?46.13%). The overall improvement achieved in rainfall generation by SRGEN is demonstrated to be effective in the improving model performance on flow and water quality output. 相似文献