The Relationship Between Exposure to Arsenic Concentrations in Drinking Water and the Development of Skin Lesions in Farmers from Inner Mongolia, China

Associations between the concentration of arsenic naturally occurring in drinking water and the development of skin lesions in people have been documented for some years at various locations around the world. Data on the exposure-response relationship between concentrations of arsenic in drinking water and prevalence of skin lesions in farmers from five locations in Inner Mongolia, China have been collected from the original publications and re-analysed together as a meta-study. The calculated data show a positive linear exposure-response relationship without a threshold. The reasons for this linear correlation are discussed and compared with the data from Xinjiang, another arsenism area located in a different geographical area of China. Here a different relationship was recorded that involved a threshold concentration before skin lesions developed. The significance of these two different exposure-response scenarios is discussed.     

Effects of Selenium Supplementation on Arsenism: An Intervention Trial in Inner Mongolia

This paper reports the effects of a placebo-controlled Se-enriched yeast supplementation trial, conducted for 14 months, on arsenism in adult farmers living in a rural community in Inner Mongolia, China. The farmers had been naturally exposed to elevated concentrations of As in drinking water from tube-wells since 1983 but changed to arsenic-free drinking water when the trial began in June 1996. Blood and hair Se and As concentrations were analysed pre-intervention and at the end of the 3rd, 9th and 14th month, while skin lesions were assessed pre-intervention, as well as at the end of the 14th month, using the Arsenism Clinical Criteria established by the Ministry of Health, China. As the trial was a voluntary one, a number of farmers did not routinely have their blood and hair samples taken for analysis. Consequently, the data have been analysed in two categories. Fifty-four farmers from the Se-group and 29 from the placebo-group who were sampled on each occasion were considered as one group, which has been compared with the second group comprising up to a total of 100 farmers in the Se-group and 86 in the placebo-group. Results calculated for those farmers who were sampled on each occasion, showed that at the end of the trial, blood and hair Se concentrations of the Se-group increased from 0.130 to 0.186 µg ml^–1 and from 0.431 to 0.502 µg g^–1, respectively, while those of the placebo-groups remained constant. Blood and hair As concentrations of the Se-group decreased from 0.051 to 0.015 µg ml^–1 and from 2.57 to 0.680 µg g^–1, respectively, a greater reduction than those in the placebo-group that went from 0.064 to 0.024 µg ml^–1 and from 2.62 to 1.25 µg g^–1, respectively. When the data from all patients were examined, the analytical trends were similar. An evaluation of skin lesions in the category who were sampled for hair and blood on each occasion showed that 41.2% of hyperkeratosis, 50.0% of depigmentation and 44.7% of pigmentation in the Se-group improved one or more degrees, while those in the placebo-group improved by only 7.1, 12.0 and 6.7%, respectively. A total of 61.1% of the adults in Se-group improved in one or more type of skin lesion, but only 17.2% improved in the placebo-group. Comparable results were obtained when all the data from both categories of farmers were examined. Results from the trial showed that Se supplementation was more effective for the improvement of adults who were affected by double or triple skin lesions. In the placebo-group, most of the severely affected adults improved in only one kind of skin lesion, but in the Se-group, more adults improved in two or three kinds of skin lesions. Although the trial was limited by its relatively small size, the results have provided some evidence of the usefulness of Se supplementation for people affected by arsenism.     

Arsenism Clinical Stages and their Relation with Hair Arsenic Concentration of Residents of Bayinmaodao Rural District, Inner Mongolia, China

The clinical skin lesions of arsenism in men and women in Bayinmaodao rural district in Inner Mongolia, Peoples Republic of China, have been examined by doctors, and their hair and drinking water samples analysed for arsenic by hydride generation and ICP-AES. Altogether 311 arsenism patients with a 15.53% prevalence rate for the district were recorded. The disease prevalence rate was positively related to population, age, and their exposure to elevated arsenic concentrations in the drinking water from 1983 when new wells were dug and drinking of surface water was abandoned. Hyperkeratosis was the most serious skin lesion with the highest occurrence rate, then depigmentation and pigmentation in decreasing order. With increasing severity of the disease, ranging from skin lesion with single hyperkeratosis 1° to hyperkeratosis 3° with depigmentation 3° and pigmentation 3°, the results showed that arsenic concentrations in head hair had increased. Arsenic concentrations in hair were positively correlated with the arsenic concentrations in drinking water obtained from local wells.     

Effects of Social Structure and Prey Dynamics on Extinction Risk in Gray Wolves

Extinction models based on diffusion theory generally fail to incorporate two important aspects of population biology—social structure and prey dynamics. We include these aspects in an individual-based extinction model for small, isolated populations of the gray wolf (Canis lupus). Our model predicts mean times to extinction significantly longer than those predicted by more general (diffusion) models. According to our model, an isolated population of 50 wolves has a 95% chance of surviving just 9 years and only a 30% chance of surviving beyond 100 years. Reflecting the influence of social structure, a wolf population initially comprising 50 individuals is expected to persist only a few years longer, on average (71 years), than is a population initially comprising just a single reproductive pair (62 years). In contrast, substantially greater average prey abundance leads to dramatically longer expected persistence times. Autocorrelated prey dynamics result in a more complex distribution of extinction times than predicted by many extinction models. We contend that demographic stochasticity may pose the greatest threat to small, isolated wolf populations, although environmental stochasticity and genetic effects may compound this threat. Our work highlights the importance of considering social structure and resource dynamics in the development of population viability analyses.     

Robust population management under uncertainty for structured population models.

Structured population models are increasingly used in decision making, but typically have many entries that are unknown or highly uncertain. We present an approach for the systematic analysis of the effect of uncertainties on long-term population growth or decay. Many decisions for threatened and endangered species are made with poor or no information. We can still make decisions under these circumstances in a manner that is highly defensible, even without making assumptions about the distribution of uncertainty, or limiting ourselves to discussions of single, infinitesimally small changes in the parameters. Suppose that the model (determined by the data) for the population in question predicts long-term growth. Our goal is to determine how uncertain the data can be before the model loses this property. Some uncertainties will maintain long-term growth, and some will lead to long-term decay. The uncertainties are typically structured, and can be described by several parameters. We show how to determine which parameters maintain long-term growth. We illustrate the advantages of the method by applying it to a Peregrine Falcon population. The U.S. Fish and Wildlife Service recently decided to allow minimal harvesting of Peregrine Falcons after their recent removal from the Endangered Species List. Based on published demographic rates, we find that an asymptotic growth rate lambda > 1 is guaranteed with 5% harvest rate up to 3% error in adult survival if no two-year-olds breed, and up to 11% error if all two-year-olds breed. If a population growth rate of 3% or greater is desired, the acceptable error in adult survival decreases to between 1% and 6% depending of the proportion of two-year-olds that breed. These results clearly show the interactions between uncertainties in different parameters, and suggest that a harvest decision at this stage may be premature without solid data on adult survival and the frequency of breeding by young adults.     

Germination and seedling development of switchgrass and smooth bromegrass exposed to 2,4,6-trinitrotoluene

It is estimated that explosives contaminate approximately 0.82 million cubic metres of soil at former military installations throughout the US; major contaminants often include 2,4,6-trinitrotoluene (TNT) and its degradation products. At some sites, phytoremediation may be a viable option to incineration or other costly remediation treatments. Grasses may be particularly suited for remediation because of their growth habit and adaptability to a wide range of soil and climate conditions. We characterized the effects of TNT on germination and early seedling development of switchgrass and smooth bromegrass to evaluate their potential use on contaminated sites. Switchgrass and smooth bromegrass seeds were germinated in nutrient-free agar containing 0 to 60 mg TNT litre(-1). Smooth bromegrass germination decreased as TNT concentration increased, while switchgrass germination was unaffected by TNT. Concentrations up to 15 mg TNT litre(-1) did not affect switchgrass root growth rate, but bromegrass root growth was reduced at TNT concentrations above 7.5 mg litre(-1). At 7.5 mg TNT litre(-1), however, shoot growth rate was reduced in both species. Examination at 20-fold magnification revealed switchgrass radicles were unaffected by TNT, while smooth bromegrass radicles appeared slightly swollen. Results indicate switchgrass is more tolerant of TNT than smooth bromegrass, but the establishment of both species may be limited to soil containing less than 50 mg kg(-1) of extractable TNT.     

Simulated effects of dryland cropping intensification on soil organic matter and greenhouse gas exchanges using the DAYCENT ecosystem model

We present evidence to show that DAYCENT can reliably simulate soil C levels, crop yields, and annual trace gas fluxes for various soils. DAYCENT was applied to compare the net greenhouse gas fluxes for soils under different land uses. To calculate net greenhouse gas flux we accounted for changes in soil organic C, the C equivalents of N2O emissions and CH4 uptake, and the CO2 costs of N fertilizer production. Model results and data show that dryland soils that are depleted of C due to conventional till winter wheat fallow cropping can store C upon conversion to no till, by reducing the fallow period, or by reversion to native vegetation. However, model results suggest that dryland agricultural soils will still be net sources of greenhouse gases although the magnitude of the source can be significantly reduced and yields can be increased upon conversion to no till annual cropping.     

Spatial distribution of tropospheric ozone in western Washington, USA

We quantified the distribution of tropospheric ozone in topographically complex western Washington state, USA (total area approximately 6000 km(2)), using passive ozone samplers along nine river drainages to measure ozone exposure from near sea level to high-elevation mountain sites. Weekly average ozone concentrations were higher with increasing distance from the urban core and at higher elevations, increasing a mean of 1.3 ppbv per 100 m elevation gain for all mountain transects. Weekly average ozone concentrations were generally highest in Cascade Mountains drainages east and southeast of Seattle (maximum=55-67 pbv) and in the Columbia River Gorge east of Portland (maximum=59 ppbv), and lowest in the western Olympic Peninsula (maximum=34 ppbv). Higher ozone concentrations in the Cascade Mountains and Columbia River locations downwind of large cities indicate that significant quantities of ozone and ozone precursors are being transported eastward toward rural wildland areas by prevailing westerly winds. In addition, temporal (week to week) variation in ozone distribution is synchronous within and between all drainages sampled, which indicates that there is regional coherence in air pollution detectable with weekly averages. These data provide insight on large-scale spatial variation of ozone distribution in western Washington, and will help regulatory agencies optimize future monitoring networks and identify locations where human health and natural resources could be at risk.