John Murimboh

Geostatistical modelling of arsenic in drinking water wells and related toenail arsenic concentrations across Nova Scotia, Canada

Arsenic is a naturally occurring class 1 human carcinogen that is widespread in private drinking water wells throughout the province of Nova Scotia in Canada. In this paper we explore the spatial variation in toenail arsenic concentrations (arsenic body burden) in Nova Scotia. We describe the regional distribution of arsenic concentrations in private well water supplies in the province, and evaluate the geological and environmental features associated with higher levels of arsenic in well water. We develop geostatistical process models to predict high toenail arsenic concentrations and high well water arsenic concentrations, which have utility for studies where no direct measurements of arsenic body burden or arsenic exposure are available. 892 men and women who participated in the Atlantic Partnership for Tomorrows Health Project provided both drinking water and toenail clipping samples. Information on socio-demographic, lifestyle and health factors was obtained with a set of standardized questionnaires. Anthropometric indices and arsenic concentrations in drinking water and toenails were measured. In addition, data on arsenic concentrations in 10,498 private wells were provided by the Nova Scotia Department of Environment. We utilised stepwise multivariable logistic regression modelling to develop separate statistical models to: a) predict high toenail arsenic concentrations (defined as toenail arsenic levels ≥0.12 μg g(-1)) and b) predict high well water arsenic concentrations (defined as well water arsenic levels ≥5.0 μg L(-1)). We found that the geological and environmental information that predicted well water arsenic concentrations can also be used to accurately predict toenail arsenic concentrations. We conclude that geological and environmental factors contributing to arsenic contamination in well water are the major contributing influences on arsenic body burden among Nova Scotia residents. Further studies are warranted to assess appropriate intervention strategies for reducing arsenic body burden among human populations.

Ecotoxicological risk assessment of undisturbed metal contaminated soil at two remote lighthouse sites.

Ecotoxicological risk assessments of contaminated soil are commonly completed using guideline values based on total concentrations. However, only certain fractions of contaminants are bioavailable and pose a hazard to the environment. This paper investigates the relationship between measured metal concentrations in soil and soil leachate, and the effects in organisms exposed to intact, undisturbed soil cores (wheat, Tricum aestivum) and soil leachate (lettuce, Lactuca sativa, and water flea, Daphnia magna). Despite the samples containing metal concentrations significantly above guideline values, metals of concern (e.g. Pb and Zn) did not have a significant toxic effect on wheat or D. magna. During weeks with low leachate pH, an effect on lettuce root elongation was observed in the most contaminated samples. This study has shown that bioassays with intact soil cores can indicate metal bioavailability and provide a better estimate of ecological risk than total metal concentrations in the soil.

What is the role of obesity in the aetiology of arsenic-related disease?

Consumption of arsenic contaminated drinking water causes a large variety of adverse health outcomes. Body mass index (BMI), which is linked to diet, is positively associated with arsenic methylation capacity. We investigated the association between an obesity-related diet and arsenic body burden from exposure to naturally contaminated drinking water among Nova Scotia residents. We collected home drinking water and toenail clipping samples among 960 men and women aged 35 to 69 years in Nova Scotia, Canada from 2009 through 2010. We measured body composition and arsenic concentrations in drinking water and toenails clipping samples and collected socio-demographic, behavioural, and dietary information via standardized questionnaires. We derived an obesity-related dietary pattern score using reduced rank regression. Across quartiles of the obesity-related dietary pattern score there were no significant differences in drinking water arsenic concentrations, but there was an inverse trend in arsenic concentrations in toenails across the dietary pattern score (P=0.01). Compared with individuals in the first quartile of the dietary pattern score, those in the second through fourth quartiles had decreased likelihoods of high toenail arsenic (≥ 85 percentile). The corresponding odds ratios (95% confidence intervals [CI]) were 0.81 (95% CI, 0.49, 1.36), 0.57 (95% CI, 0.33, 0.99), and 0.55 (95% CI, 0.31, 0.98), respectively (P for trend=0.02). We conclude that given similar levels of naturally occurring arsenic exposure via drinking water, an obesity-related dietary pattern was associated with significantly lower arsenic concentrations in toenails. Further studies to investigate the underlining mechanisms are warranted.

Bioavailability as a Factor in Risk Assessment of Metal-Contaminated Soil

To accurately assess the risks of metal contaminants in soil, the bioavailability of the metals need to be considered. The bioavailable concentrations determined from homogenized, dried soils are not necessarily representative of in situ conditions of undisturbed field soils. In this study, we investigated the accumulation of metals in wheat (Triticum aestivum) grown in undisturbed contaminated (Pb, Zn, Cu, and Cd) soil cores, in relation to total soil, leachate, and diffusive gradients in thin films (DGT)-labile metal concentrations. Despite the fact that many of the samples contained metal concentrations above guideline values, no significant effects were observed on wheat growth. The bioavailability of metals in the most contaminated samples was estimated to be medium to low, possibly explaining why few effects were observed in the bioassay. For Cu, Zn, and especially for Pb, leachate and DGT-labile concentrations were better predictors of uptake by wheat than total concentrations based on correlations. It is suggested that DGT and leachate concentrations in combination with bioassays in undisturbed soil cores can be used to account for metal bioavailability in soil. These tests could be used during the ecological risk screening stage, in conjunction with total concentrations and guideline values to better estimate receptor exposure.

Modeling the photo-oxidation of dissolved organic matter by ultraviolet radiation in freshwater lakes: implications for mercury bioavailability

Uncertainties in projected ultraviolet (UV) radiation may lead to future increases in UV irradiation of freshwater lakes. Because dissolved organic carbon (DOC) is the main binding phase for mercury (Hg) in freshwater lakes, an increase in DOC photo-oxidation may affect Hg speciation and bioavailability. We quantified the effect of DOC concentration on the rate of abiotic DOC photo-oxidation for five lakes (DOC=3.27-12.3 mg L(-1)) in Kejimkujik National Park, Canada. Samples were irradiated with UV-A or UV-B radiation over a 72-h period. UV-B radiation was found to be 2.36 times more efficient at photo-oxidizing DOC than UV-A, with energy-normalized rates of dissolved inorganic carbon (DIC) production ranging from 3.8×10(-5) to 1.1×10(-4) mg L(-1)J(-1) for UV-A, and from 6.0×10(-5) to 3.1×10(-4) mg L(-1)J(-1) for UV-B. Energy normalized rates of DIC production were positively correlated with DOC concentrations. Diffuse integrated attenuation coefficients were quantified in situ (UV-A K(d)=0.056-0.180 J cm(-1); UV-B K(d)=0.015-0.165 J cm(-1)) and a quantitative depth-integrated model for yearly DIC photo-production in each lake was developed. The model predicts that, UV-A produces between 3.2 and 100 times more DIC (1521-2851 mg m(-2) year(-1)) than UV-B radiation (29.17-746.7 mg m(-2) year(-1)). Future increases in UV radiation may increase DIC production and increase Hg bioavailability in low DOC lakes to a greater extent than in high DOC lakes.

Relationship between drinking water and toenail arsenic concentrations among a cohort of Nova Scotians.

Consumption of arsenic-contaminated drinking water is associated with increased cancer risk. The relationship between arsenic body burden, such as concentrations in human toenails, and arsenic in drinking water is not fully understood. We evaluated the relationship between arsenic concentrations in drinking water and toenail clippings among a cohort of Nova Scotians. A total of 960 men and women aged 35 to 69 years provided home drinking water and toenail clipping samples. Information on water source and treatment use and covariables was collected through questionnaires. Arsenic concentrations in drinking water and toenail clippings and anthropometric indices were measured. Private drilled water wells had higher arsenic concentrations compared with other dug wells and municipal drinking water sources (P<0.001). Among participants with drinking water arsenic levels ≥1 μg/l, there was a significant relationship between drinking water and toenail arsenic concentrations (r=0.46, P<0.0001). Given similar levels of arsenic exposure from drinking water, obese individuals had significantly lower concentrations of arsenic in toenails compared with those with a normal weight. Private drilled water wells were an important source of arsenic exposure in the study population. Body weight modifies the relationship between drinking water arsenic exposure and toenail arsenic concentrations.

Utility of bioassays (lettuce, red clover, red fescue, Microtox, MetSTICK, Hyalella, bait lamina) in ecological risk screening of acid metal (Zn) contaminated soil

The objective of this study was to assess selected bioassays and ecological screening tools for their suitability in a weight of evidence risk screening process of acidic metal contaminated soil. Intact soil cores were used for the tests, which minimizes changes in pH and metal bioavailability that may result from homogenization and drying of the soil. Soil cores were spiked with ZnCl(2) or CaCl(2). Leachate collected from the soil cores was used to account for the exposure pathways through pore water and groundwater. Tests assessed included MetSTICK in soil cores and Microtox in soil leachate, lettuce (Lactuca sativa), red fescue (Festuca rubra) and red clover (Trifolium pratense) in the soil cores and lettuce and red clover in soil leachate, Hyallella azteca in soil leachate, and an ecological soil function test using Bait Lamina in soil cores. Microtox, H. azteca, lettuce and red fescue showed higher sensitivity to low pH than to Zn concentrations and are therefore not recommended as tests on intact acidic soil cores and soil leachate. The Bait Lamina test appeared sensitive to pH levels below 3.7 but should be investigated further as a screening tool in less acidic soils. Among the bioassays, the MetSTICK and the T. pratense bioassays in soil cores were the most sensitive to Zn, with the lowest nominal NOEC of 200 and 400mg Zn/kg d.w., respectively. These bioassays were also tolerant of low pH, which make them suitable for assessing hazards of metal contaminated acid soils.

Complexation of Lead in Model Solutions of Humic Acid: Heterogeneity and Effects of Competition with Copper, Nickel, and Zinc

Environmental Context. Metal bioavailability and toxicity are often related to free metal concentration rather than total metal concentration. Humic substances are chemically and physically heterogeneous complexants for metals in natural waters, and play an important role in trace metal transport, fate, and bioavailability. Metal bioavailability, which depends on chemical speciation of metals, is greatly influenced by the presence of other trace metals and major cations in natural waters. In this work, the effects of heterogeneity of humic substances, and of competition of trace metals on lead speciation in model solutions have been studied to gain a better understanding of these effects on complexation of trace metal lead and its bioavailability. Abstract. Physicochemical heterogeneity of a well characterized humic acid (HA) in its complexation with a trace metal lead in model solutions was investigated using pseudo-polarography at a stationary mercury drop electrode, and the differential equilibrium function (DEF) of Pb(ii)–HA complexes was determined. The complexation of Pb(ii) by HA was determined by taking into account the dependence of the strength of the binding on the metal (Pb) loading. Also investigated were the effects of competition of the trace metals copper, nickel, and zinc on the DEF of Pb(ii)–HA complexes in model solutions. The results showed that these trace metals competed with trace metal lead for binding by HA even when present at the same concentrations as that of lead.

Speciation of organometals using a synchronizing GC-EIMS and GC-ICPMS system for simultaneous detection

In analytical chemistry, improvement in instrument performances is always important for achieving better analytical results and obtaining more information on the target analytes. Gas chromatography-inductively coupled plasma mass spectrometry (GC-ICPMS), which combines powerful separation ability and high sensitivity, has found broad applications in sensitive speciation of organometals such as methylmercury (MeHg), butyltin (BuSn), and seleniomethionine (SeMet). Unfortunately, GC-ICPMS is unable to provide molecular information of the analytes such as molecular fragmentations or isotopic patterns, which are very important for identifying target analytes. A method is reported for the simultaneous determination of organometals including MeHg, dibutyltin (DBT), tributyltin (TBT) and SeMet using a unique interface with gas chromatography-electron ionization mass spectrometry (GC-EIMS) and GC-ICPMS systems synchronously. The method was validated with measurements of MeHg, DBT, TBT and SeMet in the certified reference materials (CRMs) including dogfish liver (DOLT-4), marine sediments (PACS-2) and selenium-enriched yeast (SELM-1). Compared with EIMS, ICPMS achieved a remarkable gain in sensitivity for MeHg, DBT and SeMet (19-, 130- and 2850-fold S/N gain, respectively). The concentrations of MeHg (1.335 ± 0.033 μg g−1), DBT (1.171 ± 0.005 μg g−1) and TBT (0.834 ± 0.003 μg g−1) obtained with isotope dilution are in agreement with the certified values of the corresponding CRMs. With the proposed method, the ICPMS system can provide higher precision and sensitivity, and the EIMS system can provide information on the molecular structure, which is essential for identification of target analytes.

The influence of avian biovectors on mercury speciation in a bog ecosystem

Methylmercury (MeHg) is a neurotoxin and endocrine disruptor that bioaccumulates and biomagnifies through trophic levels, resulting in potentially hazardous concentrations. Although wetlands are known hotspots for mercury (Hg) methylation, the effects of avian biovectors on these processes are poorly understood. We examined Hg speciation and distribution in shallow groundwater and surface water from a raised-bog with over 30years of avian biovector (herring gulls Larus argentatus and great black-backed gulls Larus marinus) colonization and guano input. Compared to the reference site, the avian-impacted bog had elevated concentrations of total dissolved organic carbon (TOC), total Hg, MeHg, phosphate (PO43-), and other trace metals, notably Pb, As, Cd and Ni. Spatial interpolation showed that the densest area of gull nesting was co-located with areas that had the highest concentrations of PO43-, MeHg, As and Cd, but not total mercury (THg), and models suggested that Mn, PO43-, and dissolved TOC were strong predictors of MeHg. Our findings suggest that while these gulls may not be a significant source of Hg, the excess of PO43- (a well recognised component of guano) and the subsequent changes in water chemistry due to avian biovector subsidies may increase net Hg methylation.