Quantitative tolerance values for common stream benthic macroinvertebrates in the Yangtze River Delta,Eastern China

Aquatic organisms’ tolerance to water pollution is widely used to monitor and assess freshwater ecosystem health. Tolerance values (TVs) estimated based on statistical analyses of species-environment relationships are more objective than those assigned by expert opinion. Region-specific TVs are the basis for developing accurate bioassessment metrics particularly in developing countries, where both aquatic biota and their responses to human disturbances have been poorly documented. We used principal component analysis to derive a synthetic gradient for four stressor variables (total nitrogen, total phosphorus, dissolved oxygen, and % silt) based on 286 sampling sites in the Taihu Lake and Qiantang River basins (Yangtze River Delta), China. We used the scores of taxa on the first principal component (PC1), which explained 49.8 % of the variance, to estimate the tolerance values (TV_r) of 163 macroinvertebrates taxa that were collected from at least 20 sites, 81 of which were not included in the Hilsenhoff TV lists (TV_h) of 1987. All estimates were scaled into the range of 1–10 as in TV_h. Of all the taxa with different TVs, 46.3 % of TV_r were lower and 52.4 % were higher than TV_h. TV_r were significantly (p?<?0.01, Fig. 2), but weakly (r ²?=?0.34), correlated with TV_h. Seven biotic metrics based on TV_r were more strongly correlated with the main stressors and were more effective at discriminating references sites from impacted sites than those based on TV_h. Our results highlight the importance of developing region-specific TVs for macroinvertebrate-based bioassessment and to facilitate assessment of streams in China, particularly in the Yangtze River Delta.     

Assessment of the bioavailability of cadmium in Jamaican soils

Extraordinary geogenic concentrations of cadmium (Cd) have been reported for some Jamaican soils. However, the bioavailability of the metal in these soils remains unknown. Here, the bioavailability of Cd in selected Jamaican soils was investigated through the determination of total and sequentially extractable concentrations in paired soil–plant (yam; Dioscorea sp.) samples (n?=?24), using neutron activation analysis and atomic absorption spectroscopy as primary analytical techniques. Our results indicate that total soil Cd varied widely (2.2–148.7 mg kg^?1), and on average, total extractable Cd accounted for ~55 % of the total soil Cd. The exchangeable and oxidizable species averaged 1.5 and 6.4 % of the total Cd, respectively, and, based on Spearman analysis, are the best predictors of yam Cd. There is also good evidence to suggest that variation in the bioavailability of the metal is in part controlled by the geochemical characteristics of the soils analyzed and is best explained by pH, cation exchange capacity (CEC) and organic matter content (% LOI).     

Visually determined stream mesohabitats influence benthic macroinvertebrate assessments in headwater streams

Mesohabitat components such as substrate and surface flow types are intimately related to benthic macroinvertebrate assemblages in streams. Visual assessments of the distribution of these components provide a means of evaluating physical habitat heterogeneity and aid biodiversity surveys and monitoring. We determined the degree to which stream site and visually assessed mesohabitat variables explain variability (i.e., beta-diversity) in the relative abundance and presence-absence of all macroinvertebrate families and of Ephemeroptera, Plecoptera, and Trichoptera (EPT) genera. We systematically sampled a wide variety of mesohabitat arrangements as they occured in stream sites. We also estimated how much of the explanation given by mesohabitat was associated with substrate or surface flow types. We performed variation partitioning to determine fractions of explained variance through use of partial redundancy analysis (pRDA). Mesohabitats and stream sites explained together from 23 to 32 % of the variation in the four analyses. Stream site explained 8–11 % of that variation, and mesohabitat variables explained 13–20 %. Surface flow types accounted for >60 % of the variation provided by the mesohabitat component. These patterns are in accordance with those obtained in previous studies that showed the predominance of environmental variables over spatial location in explaining macroinvertebrate distribution. We conclude that visually assessed mesohabitat components are important predictors of assemblage composition, explaining significant amounts of beta-diversity. Therefore, they are critical to consider in ecological and biodiversity assessments involving macroinvertebrates.     

Assessment of pumped mercury vapour adsorption tubes as passive samplers using a micro-exposure chamber

Mercury vapour adsorption tubes manufactured for pumped sampling and analysis have been evaluated for their performance as passive samplers. This has been done by exposing these tubes in a novel micro-exposure chamber. The uptake rates of these tubes have been found to be low (approximately 0.215 ml min(-1)) as compared to bespoke passive samplers for mercury vapour (typically in excess of 50 ml min(-1)). The measured uptake rates were shown to vary significantly between tubes and this was attributed to the variability in the air-sorbent interface and the proportion of the cross sectional area removed by the crimp in the quartz tubes used to secure the sorbent material. As a result of this variability the uptake rate of each tube must be determined using the micro-exposure chamber prior to deployment. Results have shown that the uptake rate determined in the micro-exposure chamber is invariant of concentration, and therefore these uptakes rates may be determined at a high mercury vapour concentration for many tubes at once in less than one hour. The uptake rate of the adsorption tubes under these conditions may be determined with a precision of 5%. Measurements made on a limited field trial in indoor and outdoor ambient air have shown that these tubes give results in acceptable agreement with more traditional pumped sampling methods, although longer sampling periods are required in order to reduce the uncertainty of the measurement, which is currently approximately 30%.     

Approaches to systematic assessment of environmental exposures posed at hazardous waste sites in the developing world: the Toxic Sites Identification Program

In the developing world, environmental chemical exposures due to hazardous waste sites are poorly documented. We describe the approach taken by the Blacksmith Institute's Toxic Sites Identification Program in documenting environmental chemical exposures due to hazardous waste sites globally, identifying sites of concern and quantifying pathways, populations, and severity of exposure. A network of local environmental investigators was identified and trained to conduct hazardous waste site investigations and assessments. To date, 2,095 contaminated sites have been identified within 47 countries having an estimated population at risk of 71,500,000. Trained researchers and investigators have visited 1,400 of those sites. Heavy metals are the leading primary exposures, with water supply and ambient air being the primary routes of exposure. Even though chemical production has occurred largely in the developed world to date, many hazardous waste sites in the developing world pose significant hazards to the health of large portions of the population. Further research is needed to quantify potential health and economic consequences and identify cost-effective approaches to remediation.     

The problem of using fixed-area subsampling methods to estimate macroinvertebrate richness: a case study with Neotropical stream data

Subsampling has been widely applied in the laboratory to process freshwater macroinvertebrate samples. Currently, many governmental agencies and research groups apply the fixed-count approach, targeting a number of individuals per sample, and at the same time keeping track of the number of quadrats (fraction of the sample) processed. However, fixed-area methods are still in use. The objective of this paper was to evaluate the reliability of macroinvertebrate taxonomic richness estimates developed from processing a standard number of subsampling quadrats (i.e., fixed-area approaches). We used a dataset from 18 tropical stream sites experiencing three different levels of human disturbance (most-, intermediate-, and least-disturbed). With 12 quadrats processed (half the sample), the collection curves started to stabilize, and for more than half of the sites studied, it was possible to sample at least 80 % of the total taxonomic richness of the sample. However, we observed that the minimum number of quadrats to achieve 80 % of taxonomic richness was strongly negatively correlated with the number of individuals collected in each site: the fewer the individuals in a sample, the greater the processed proportion of that sample needed to represent it properly. Thus our results indicate that for any given areal subsampling effort (any fixed fraction of the sample), samples with different numbers of individuals will be represented differently in terms of the proportion of the total number of taxa of the whole samples, those with greater numbers being overestimated and those with fewer numbers being underestimated. Therefore, we do not recommend the use of fixed-area subsampling methods alone if the main purpose is to measure and analyze taxonomic richness; instead, we encourage researchers to use fixed-count approaches for this purpose.     

Assessment of potential health risk for inhabitants living near a former lead smelter. Part 2: site-specific human health risk assessment of Cd and Pb contamination in kitchen gardens

Metal contamination of urban soils and homegrown products has caused major concern. In Part 1, we investigated the long-term effects of a former smelter on the degree of kitchen garden-soil contamination and the quality of the homegrown vegetables from these gardens. The results showed that the soils retained a high level of contamination and that a large proportion of the vegetables produced did not comply with the legislation on the levels of metals allowed for human consumption. The present study aims to assess the associated potential health risk to local inhabitants through consumption of homegrown vegetables and ingestion of soil particles using a land use-based approach. For lead (Pb), the standard hazard quotient (HQ)-based risk assessment method was used to determine the HQ. For cadmium (Cd), the approach consisted of calculating the HQs and then deriving site-specific assessment criteria (SSAC) using the SNIFFER method. The results suggested that the exposure pathways considered should not engender any form of deleterious health effects for adults. For children, Pb was the main concern and induced a relatively high health risk through soil particle ingestion, and most total soil Cd concentrations exceeded the derived SSAC, in particular, through consumption of vegetables. The metal bioaccessibility in soils was incorporated into the methods to establish more realistic risk assessment measures. This study proposes an approach to integrate different human health risk assessment methods. Further investigations should complete the assessment to improve risk determination, e.g., the determination of metal bioaccessibility in vegetables.     

Vector-Borne Diseases, Development & Climate Change

Vector-borne diseases are feared to extend their range in a future where global warming has occurred. There is considerable concern about scourges such as malaria re-invading currently temperate regions and reaching into higher altitudes in Africa. In this paper we examine the various factors thought to determine potential infectivity of malaria, and its actual outbreak in the context of a dynamic integrated assessment model. We quantify: (i) the role of demographics in placing a larger population in harms way; (ii) the role of climate change in increasing the potential geographic range and severity of the risk of infection; and (iii) the role of economic and social development in limiting the occurrence of malaria. We then explore the climate and economic implications of various climate policies in their effectiveness to limit potential infectivity of malaria. In illustration of these issues we present the climate-related and economics-related impacts of unilateral CO₂ control by OECD on incidence of malaria in non-OECD nations. The model presented here, although highly stylized in its representation of socio-economic factors, provides strong evidence of the role of socio-economic factors in determination of malaria incidence. The case study offers insights into unintended adverse consequences of well-meaning climate policies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Lead forms in urban turfgrass and forest soils as related to organic matter content and pH

Identification of reference streams and human disturbance gradients are crucial steps in assessing the effects of human disturbances on stream health. We describe a process for identifying reference stream reaches and assessing disturbance gradients using readily available, geo-referenced stream and human disturbance databases. We demonstrate the utility of this process by applying it to wadeable streams in Michigan, USA, and use it to identify which human disturbances have the greatest impact on streams. Approximately 38% of cold-water and 16% of warm-water streams in Michigan were identified as being in least-disturbed condition. Conversely, approximately 3% of cold-water and 4% of warm-water streams were moderately to severely disturbed by landscape human disturbances. Anthropogenic disturbances that had the greatest impact on moderately to severely disturbed streams were nutrient loading and percent urban land use within network watersheds. Our process for assessing stream health represents a significant advantage over other routinely used methods. It uses inter-confluence stream reaches as an assessment unit, permits the evaluation of stream health across large regions, and yields an overall disturbance index that is a weighted sum of multiple disturbance factors. The robustness of our approach is linked to the scale of disturbances that affect a stream; it will be less robust for identifying less degraded or reference streams with localized human disturbances. With improved availability of high-resolution disturbance datasets, this approach will provide a more complete picture of reference stream reaches and factors contributing to degradation of stream health.     

Continuous and filter-based measurements of PM2.5 nitrate and sulfate at the Fresno Supersite

PM(2.5) nitrate [Formula: see text] and sulfate ([Formula: see text]) were measured continuously with R&P8400N and R&P8400S instruments, respectively, and compared with filter-based measurements at the Fresno Supersite from October, 2000 through December, 2005. [Formula: see text] concentrations were higher in winter than summer with a long-term decreasing trend. Correlations between 24-h average continuous and filter-based [Formula: see text] were greater than 0.96 in 4 out of 5 years. Continuous [Formula: see text] was generally lower than filter-based [Formula: see text] although the difference decreased over time, from -52% in 2001 to +13% in 2005. These differences were similar in winter (-23%) and summer (-19%) while the corresponding differences between ambient and instrument temperature were -12 and 0.7 degrees C, respectively. Neither seasonal nor long-term trends in [Formula: see text] can be explained by variations in ambient temperature, the difference between ambient and instrument temperature, or changes in aerosol chemical composition. There were no seasonal or long-term trends in [Formula: see text] concentrations, partially due to low concentrations observed in Fresno. Long-term variability in the performance of R&P8400 [Formula: see text] and [Formula: see text] instruments suggest that collocation with filter measurements is needed for long-term measurements.