Longitudinal investigation of exposure to arsenic, cadmium, and lead in drinking water.
(49/2380)
Arsenic, cadmium, and lead have been associated with various forms of cancer, nephrotoxicity, central nervous system effects, and cardiovascular disease in humans. Drinking water is a well-recognized pathway of exposure to these metals. To improve understanding of the temporal dimension of exposure to As, Cd, and Pb in drinking water, we obtained 381 samples of tap and/or tap/filtered water and self-reported rates of drinking water consumption from 73 members of a stratified random sample in Maryland. Data were collected at approximately 2-month intervals from September 1995 through September 1996. Concentrations of As (range < 0.2-13.8 microg/L) and Pb (< 0.1-13.4 microg/L) were within the ranges reported for the United States, as were the rates of drinking water consumption (median < 0.1-4.1 L/day). Cd was present at a detectable level in only 8.1% of the water samples. Mean log-transformed concentrations and exposures for As and Pb varied significantly among sampling cycles and among respondents, as did rates of drinking water consumption, according to a generalized linear model that accounted for potential correlation among repeated measures from the same respondent. We used the intraclass correlation coefficient of reliability to attribute the total variance observed for each exposure metric to between-person and within-person variability. Between-person variability was estimated to account for 67, 81, and 55% of the total variance in drinking water consumption, As exposure (micrograms per day), and Pb exposure (micrograms per day), respectively. We discuss these results with respect to their implications for future exposure assessment research, quantitative risk assessment, and environmental epidemiology. (+info)
Toluene-degrading bacteria are chemotactic towards the environmental pollutants benzene, toluene, and trichloroethylene.
(50/2380)
The bioremediation of polluted groundwater and toxic waste sites requires that bacteria come into close physical contact with pollutants. This can be accomplished by chemotaxis. Five motile strains of bacteria that use five different pathways to degrade toluene were tested for their ability to detect and swim towards this pollutant. Three of the five strains (Pseudomonas putida F1, Ralstonia pickettii PKO1, and Burkholderia cepacia G4) were attracted to toluene. In each case, the response was dependent on induction by growth with toluene. Pseudomonas mendocina KR1 and P. putida PaW15 did not show a convincing response. The chemotactic responses of P. putida F1 to a variety of toxic aromatic hydrocarbons and chlorinated aliphatic compounds were examined. Compounds that are growth substrates for P. putida F1, including benzene and ethylbenzene, were chemoattractants. P. putida F1 was also attracted to trichloroethylene (TCE), which is not a growth substrate but is dechlorinated and detoxified by P. putida F1. Mutant strains of P. putida F1 that do not oxidize toluene were attracted to toluene, indicating that toluene itself and not a metabolite was the compound detected. The two-component response regulator pair TodS and TodT, which control expression of the toluene degradation genes in P. putida F1, were required for the response. This demonstration that soil bacteria can sense and swim towards the toxic compounds toluene, benzene, TCE, and related chemicals suggests that the introduction of chemotactic bacteria into selected polluted sites may accelerate bioremediation processes. (+info)
A 90-day drinking water toxicity study in rats of the environmental contaminant ammonium perchlorate.
(51/2380)
Perchlorate (ClO(4)(-)), the dissociated anion of perchlorate salts such as ammonium, potassium, and sodium perchlorate, has been recently recognized as a persistent and pervasive contaminant of drinking water supplies in a number of metropolitan areas. Perchlorate is of concern because of uncertainties in the toxicological database available to address the potential human health effects of low-level exposure. The purpose of this study was to evaluate the subchronic toxicity of perchlorate when administered to Sprague-Dawley rats as ammonium perchlorate (AP) for 14 or 90 days. The study consisted of an untreated control group and five treatment groups that received continuous exposure to AP via the drinking water at dosage levels of 0.01, 0.05, 0.2, 1.0, and 10.0 mg/kg/day. The study design included a nontreatment recovery period of 30 days to evaluate the reversibility of any AP-induced effects at the 0.05, 1.0, and 10.0 mg/kg/day levels. The study also investigated the potential effects of AP on male sperm parameters, female estrous cyclicity, bone marrow micronucleus formation, and serum hormone levels, i.e., triiodothyronine (T(3)), thyroxine (T(4)), and thyroid stimulating hormone (TSH). No toxicologically meaningful differences were observed between the control and AP-treated groups with respect to survival, clinical observations, body weights, food consumption, water consumption, ophthalmology, hematology, clinical chemistry, estrous cycling, sperm parameters, or bone marrow micronucleus formation. A target organ effect was produced by AP in the thyroids of male and female rats at the 10 mg/kg/day level after 14 and 90 days of exposure. The effect was characterized by significantly increased thyroid weights and thyroid histopathology consisting primarily of follicular cell hypertrophy with microfollicle formation and colloid depletion. These changes were reversible after a nontreatment recovery period of 30 days. Statistically significant changes in TSH and thyroid hormones were observed at all AP dosage levels tested; however, no thyroid organ weight or histopathological effects were observed at AP dosage levels < or = 1.0 mg/kg/day. In the absence of thyroid organ weight and histopathological effects, the toxicological significance of TSH and thyroid hormone changes at AP dosage levels < or = 1.0 mg/kg/day remains to be determined. (+info)
New isotopic evidence for chronic lead contamination in the San Francisco Bay estuary system: implications for the persistence of past industrial lead emissions in the biosphere.
(52/2380)
Measurements of lead isotope compositions in unfiltered San Francisco Bay waters from 1989 to 1998 have brought new insights into the cycling of anthropogenic lead in estuaries. Isotopic compositions of lead in the shallow (<2 m) southern reach were essentially invariant ( approximately 90% derived from 1960s-1970s leaded gasoline) during the study period because of limited hydraulic flushing and the remobilization of lead from bottom sediments. In contrast, in the northern reach freshwater flushing from the San Joaquin and Sacramento rivers produced seasonal and decadal variations in lead isotope compositions. The seasonal shifts are attributed to advection of soils containing late 1980s gasoline lead into the bay during winter rains. Mass balance calculations indicate that only a small fraction (1-10%) of this leaded gasoline fallout from the late 1980s has been washed out of the San Joaquin and Sacramento rivers' drainage basin by 1995. Superimposed on this seasonal cycling was a long-term systematic shift in the component of gasoline lead expressed in the river systems, with a small ( approximately 5-10%) decrease in the amount of 1960s-1970s gasoline lead in river and North Bay waters. The retention of gasoline lead in the river systems draining into the bay as well as San Francisco Bay sediments indicates that historic gasoline deposits may remain in the combined riparian/estuarine system for decades. Such a persistence is in contraindication to recent reports of rapid (annual) decreases in lead contamination in other environments, and the link between climate and contaminant transport suggests local or global climate change will have an impact on contaminant distribution and fate. (+info)
Developmental and tissue-specific expression of AHR1, AHR2, and ARNT2 in dioxin-sensitive and -resistant populations of the marine fish Fundulus heteroclitus.
(53/2380)
Fundulus heteroclitus is a well-characterized marine fish model for studying aryl hydrocarbon toxicity. The F. heteroclitus population in New Bedford Harbor (NBH), a Superfund site in southeastern Massachusetts, exhibits heritable resistance to the toxic effects of planar halogenated aromatic hydrocarbons (PHAHs), including 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyls (PCBs). To investigate the role of the aryl hydrocarbon receptor (AHR) signal transduction pathway in PHAH resistance, we measured the relative levels of AHR1, AHR2, and ARNT2 mRNA in whole embryos at different developmental stages and in dissected tissues of adults, comparing expression of these genes in NBH fish with fish from a reference site (Scorton Creek, MA [SC]). Expression of both AHR1 and AHR2 mRNA increased during development, achieving maximum levels prior to hatching. Maximal embryonic expression of AHR1 was delayed relative to AHR2. Whole NBH and SC embryos exhibited no discernable differences in expression of these genes. As we have previously observed, adult SC fish expressed AHR2 and ARNT2 mRNA in all tissues examined, while AHR1 was expressed predominantly in brain, heart, and gonads. In contrast, AHR1 mRNA was widely expressed in NBH fish, appearing with unusual abundance in gill, gut, kidney, liver, and spleen. This AHR1 expression pattern was not observed in the lab-reared progeny of NBH fish, demonstrating that constitutive AHR1 expression in gill, gut, kidney, liver, and spleen is not a heritable phenotype. Furthermore, widespread AHR1 expression was not induced in reference-site fish by TCDD or PCB mixtures, suggesting that aberrant AHR1 expression is not simply a normal physiological response of contaminant exposure. These results identify ubiquitous AHR1 expression as an attribute unique to feral NBH F. heteroclitus, and they represent a first step in determining the regulatory mechanisms underlying this expression pattern and its possible role in TCDD resistance. (+info)
Contamination of drinking-water by arsenic in Bangladesh: a public health emergency.
(54/2380)
The contamination of groundwater by arsenic in Bangladesh is the largest poisoning of a population in history, with millions of people exposed. This paper describes the history of the discovery of arsenic in drinking-water in Bangladesh and recommends intervention strategies. Tube-wells were installed to provide "pure water" to prevent morbidity and mortality from gastrointestinal disease. The water from the millions of tube-wells that were installed was not tested for arsenic contamination. Studies in other countries where the population has had long-term exposure to arsenic in groundwater indicate that 1 in 10 people who drink water containing 500 micrograms of arsenic per litre may ultimately die from cancers caused by arsenic, including lung, bladder and skin cancers. The rapid allocation of funding and prompt expansion of current interventions to address this contamination should be facilitated. The fundamental intervention is the identification and provision of arsenic-free drinking water. Arsenic is rapidly excreted in urine, and for early or mild cases, no specific treatment is required. Community education and participation are essential to ensure that interventions are successful; these should be coupled with follow-up monitoring to confirm that exposure has ended. Taken together with the discovery of arsenic in groundwater in other countries, the experience in Bangladesh shows that groundwater sources throughout the world that are used for drinking-water should be tested for arsenic. (+info)
A small-volume bioassay for quantification of the esterase inhibiting potency of mixtures of organophosphate and carbamate insecticides in rainwater: development and optimization.
(55/2380)
The goal of this study was to develop a sensitive in vitro bioassay for quantification of the total esterase inhibiting potency of low concentrations of organophosphate and carbamate insecticides in relatively small rainwater samples. Purified acetylcholinesterase (AChE) from electric eel (Electrophorus electricus) and carboxylesterases from a homogenate of honeybee heads (Apis mellifera) were used as esterases, each having different affinities for the substrates S-acetylthiocholine-iodide (ATC) and N-methylindoxylacetate (MIA). MIA hydrolysis by honeybee homogenate was more sensitive to inhibition by organophosphate insecticides than ATC hydrolysis by purified AChE, although the latter parameter is often used for in vitro monitoring of esterase inhibitors. The higher sensitivity of carboxylesterases is attributed to the instant formation of a reversible Michaelis-Menten complex with the inhibitor, which competes with MIA for the active sites of the free enzymes. This dose-dependent instant inhibition can be quantified with kinetics for competitive inhibition at dichlorvos concentrations < 16 nM. At similar concentrations, purified AChE was not instantly inhibited, whereas both AChE and carboxylesterases were irreversibly and progressively inhibited at higher dichlorvos concentrations (IC50(10min) >/= 0.1 microM). Honeybee homogenate mediated MIA hydrolysis was applied as the most sensitive enzyme-substrate combination for experiments with fractionated extracts of 4 rainwater samples collected in a natural conservation area. Most esterase inhibiting potency was found in the polar methanol fraction, with recalculated concentrations equivalent to 12-125 ng dichlorvos per liter rainwater. (+info)
Bacterial biodegradation of extractives and patterns of bordered pit membrane attack in pine wood.
(56/2380)
Wood extractives, commonly referred to as pitch, cause major problems in the manufacturing of pulp and paper. Treatment of nonsterile southern yellow pine chips for 14 days with Pseudomonas fluorescens, Pseudomonas sp., Xanthomonas campestris, and Serratia marcescens reduced wood extractives by as much as 40%. Control treatments receiving only water lost 11% of extractives due to the growth of naturally occurring microorganisms. Control treatments were visually discolored after the 14-day incubation, whereas bacterium-treated wood chips were free of dark staining. Investigations using P. fluorescens NRRL B21432 showed that all individual resin and fatty acid components of the pine wood extractives were substantially reduced. Micromorphological observations showed that bacteria were able to colonize resin canals, ray parenchyma cells, and tracheids. Tracheid pit membranes within bordered pit chambers were degraded after treatment with P. fluorescens NRRL B21432. P. fluorescens and the other bacteria tested appear to have the potential for biological processing to substantially reduce wood extractives in pine wood chips prior to the paper making process so that problems associated with pitch in pulp mills can be controlled. (+info)