Elemental concentrations and in vitro bioaccessibility in Canadian background soils

Elemental concentrations and bioaccessibility were determined in background soils collected in Canada as part of the North American Geochemical Landscapes Project. The concentrations of As, Cr, Cu, Co, Ni and Zn were higher in the C-horizon (parent material) compared to 0-5 cm (surface soil), and this observation along with the regional distribution suggested that most of the variability in concentrations of these elements were governed by the bedrock characteristics. Unlike the above-stated elements, Pb and Cd concentrations were higher in the surface layer reflecting the potential effects of anthropogenic deposition. Elemental bioaccessibility was variable decreasing in the order Cd > Pb > Cu > Zn > Ni > Co > As > Cr for the surface soils. With the exception of As, bioaccessibility was generally higher in the C-horizon soils compared to the 0-5 cm soils. The differences in metal bioaccessibility between the 0-5 cm and the C-horizon and among the provinces may reflect geological processes and speciation. The mean, median or 95th percentile bioaccessibility for As, Cr, Cu, Co, Ni and Pb were all below 100 %, suggesting that the use of site-specific bioaccessibility results for these elements will yield more accurate estimation of the risk associated with oral bioavailability for sites where soil ingestion is the major contributor of human health risk.

Assessment of exposures and potential risks to the US adult population from the leaching of elements from gold and ceramic dental restorations

Using data from the 2001 to 2004 US National Health and Nutrition Examination Survey (NHANES) on the number and placement of tooth restorations in adults, we quantified daily doses due to leaching of elements from gold (Au) alloy and ceramic restorative materials. The elements with the greatest leaching rates from these materials are often the elements of lowest proportional composition. As a result, exposure due to wear will predominate for those elements of relatively high proportional composition, while exposure due leaching may predominate for elements of relatively low proportional composition. The exposure due to leaching of silver (Ag) and palladium (Pd) from Au alloys exceeded published reference exposure levels (RELs) for these elements when multiple full surface crowns were present. Six or more molar crowns would result in exceeding the REL for Ag, whereas three or more crowns would be necessary to exceed the REL for Pd. For platinum (Pt), the majority of tooth surfaces, beyond just molar crowns, would be necessary to exceed the REL for Pd. Exposures due to leaching of elements from ceramic dental materials were less than published RELs for all components examined here, including having all restorations composed of ceramic.

Assessment of exposures and potential risks to the US adult population from wear (attrition and abrasion) of gold and ceramic dental restorations

Little has been published on the chemical exposures and risks of dental restorative materials other than from dental amalgam and composite resins. Here we provide the first exposure and risk assessment for gold (Au) alloy and ceramic restorative materials. Based on the 2001-2004 US National Health and Nutrition Examination Survey (NHANES), we assessed the exposure of US adults to the components of Au alloy and ceramic dental restorations owing to dental material wear. Silver (Ag) is the most problematic component of Au alloy restorations, owing to a combination of toxicity and proportional composition. It was estimated that adults could possess an average of four tooth surfaces restored with Au alloy before exceeding, on average, the reference exposure level (REL) for Ag. Lithium (Li) is the most problematic component of dental ceramics. It was estimated that adults could possess an average of 15 tooth surfaces restored with ceramics before exceeding the REL for Li. Relative risks of chemical exposures from dental materials decrease in the following order: Amalgam>Au alloys>ceramics>composite resins.

Mercury exposure and risks from dental amalgam in the US population, post-2000

Dental amalgam is 50% metallic mercury (Hg) by weight and Hg vapour continuously evolves from in-place dental amalgam, causing increased Hg content with increasing amalgam load in urine, faeces, exhaled breath, saliva, blood, and various organs and tissues including the kidney, pituitary gland, liver, and brain. The Hg content also increases with maternal amalgam load in amniotic fluid, placenta, cord blood, meconium, various foetal tissues including liver, kidney and brain, in colostrum and breast milk. Based on 2001 to 2004 population statistics, 181.1 million Americans carry a grand total of 1.46 billion restored teeth. Children as young as 26 months were recorded as having restored teeth. Past dental practice and recently available data indicate that the majority of these restorations are composed of dental amalgam. Employing recent US population-based statistics on body weight and the frequency of dentally restored tooth surfaces, and recent research on the incremental increase in urinary Hg concentration per amalgam-filled tooth surface, estimates of Hg exposure from amalgam fillings were determined for 5 age groups of the US population. Three specific exposure scenarios were considered, each scenario incrementally reducing the number of tooth surfaces assumed to be restored with amalgam. Based on the least conservative of the scenarios evaluated, it was estimated that some 67.2 million Americans would exceed the Hg dose associated with the reference exposure level (REL) of 0.3 μg/m(3) established by the US Environmental Protection Agency; and 122.3 million Americans would exceed the dose associated with the REL of 0.03 μg/m(3) established by the California Environmental Protection Agency. Exposure estimates are consistent with previous estimates presented by Health Canada in 1995, and amount to 0.2 to 0.4 μg/day per amalgam-filled tooth surface, or 0.5 to 1 μg/day/amalgam-filled tooth, depending on age and other factors.

An interagency comparison of screening-level risk assessment approaches

Approaches to risk assessment have been shown to vary among regulatory agencies and across jurisdictional boundaries according to the different assumptions and justifications used. Approaches to screening-level risk assessment from six international agencies were applied to an urban case study focusing on benzo[a]pyrene (B[a]P) exposure and compared in order to provide insight into the differences between agency methods, assumptions, and justifications. Exposure estimates ranged four-fold, with most of the dose stemming from exposure to animal products (8-73%) and plant products (24-88%). Total cancer risk across agencies varied by two orders of magnitude, with exposure to air and plant and animal products contributing most to total cancer risk, while the air contribution showed the greatest variability (1-99%). Variability in cancer risk of 100-fold was attributed to choices of toxicological reference values (TRVs), either based on a combination of epidemiological and animal data, or on animal data. The contribution and importance of the urban exposure pathway for cancer risk varied according to the TRV and, ultimately, according to differences in risk assessment assumptions and guidance. While all agency risk assessment methods are predicated on science, the study results suggest that the largest impact on the differential assessment of risk by international agencies comes from policy and judgment, rather than science.

Is house dust the missing exposure pathway for PBDEs? An analysis of the urban fate and human exposure to PBDEs

Polybrominated diphenyl ether (PBDE) body burdens in North America are 20 times that of Europeans and some "high accumulation" individuals have burdens up to 1-2 orders of magnitude higher than median values, the reasons for which are not known. We estimated emissions and fate of sigma PBDEs (minus BDE-209) in a 470 km2 area of Toronto, Canada, using the Multi-media Urban Model (MUM-Fate). Using a combination of measured and modeled concentrations for indoor and outdoor air, soil, and dust plus measured concentrations in food, we estimated exposure to sigma PBDEs via soil, dust, and dietary ingestion and indoor and outdoor inhalation pathways. Fate calculations indicate that 57-85% of PBDE emissions to the outdoor environment originate from within Toronto and that the dominant removal process is advection by air to downwind locations. Inadvertent ingestion of house dust is the largest contributor to exposure of toddlers through to adults and is thus the main exposure pathway for all life stages other than the infant, including the nursing mother, who transfers PBDEs to her infant via human milk. The next major exposure pathway is dietary ingestion of animal and dairy products. Infant consumption of human milk is the largest contributor to lifetime exposure. Inadvertent ingestion of dust is the main exposure pathway for a scenario of occupational exposure in a computer recycling facility and a fish eater. Ingestion of dust can lead to almost 100-fold higher exposure than "average" for a toddler with a high dust intake rate living in a home in which PBDE concentrations are elevated.

Derivation of an ambient water quality criterion for mercury: taking account of site-specific conditions

Mercury is considered to be a serious risk to wildlife. As a result, the Great Lakes Water Quality Initiative and others have developed ambient water quality criteria (AWQC) for the protection of wildlife. These AWQC have been controversial, however, because the AWQC were single values that did not account for site-specific conditions, derivation of the AWQC relied on a single no-observed-adverse-effect level, and the AWQC had an unknown level of conservatism because of reliance on both average and conservative assumptions and uncertainty factors. Rather than develop a single-value AWQC for total mercury, we derived an AWQC model that explicitly incorporates factors controlling bioavailability, methylation rates, and bioaccumulation in the aquatic environment (e.g., pH, dissolved organic carbon). To derive our AWQC model, field data were collected from 31 lakes in Ontario and an additional 10 lakes in Nova Scotia (North America). In the field study, levels of total and methylmercury in water and fish as well as levels of key water quality variables were determined. We conducted multiple-regression analysis to derive a model that estimates mercury levels in prey of mink. Mink are very sensitive to mercury exposure. An independent dataset consisting of 51 water bodies in the United States was then used to confirm the validity and robustness of the AWQC model. Next, we combined the results of chronic-feeding studies with similar protocols and endpoints in a meta-analysis to derive a dose-response curve for mink exposed to mercury in the diet. In the final step, we used a probabilistic risk model to estimate the concentrations of methylmercury in water that would lead to levels in fish sufficient for a 10% probability of exceeding the lethal dose affecting 5% of the mink population. The result is an AWQC equation for mercury for the protection of wildlife that can be used with a variety of site-specific conditions.

Nursing assessment: impact on type and cost of interventions to prevent pressure ulcers

OBJECTIVE

To describe pressure ulcer preventive interventions and their cost, and to compare the preventive intervention use and cost with level of risk.

DESIGN

Comparative, descriptive design.

SETTING AND SUBJECTS

A large midwestern Veteran's Affairs Medical Center with 260 long-term care beds. Thirty-one chair- or bed-bound residents from 1 long-term care unit comprised the study sample.

MAIN OUTCOME MEASURES

The outcome variables included demographic information (patient record), Braden Risk Assessment score, institutional risk assessment score (Pressure Ulcer Risk Tool), type and frequency of preventive interventions, and the related costs.

METHODS

Subjects were assessed on a weekly basis for type and frequency of preventive intervention and for the development of a pressure ulcer. Each subject was observed until death, discharge, pressure ulcer formation, or the end of the 3-month study period.

RESULTS

The 3-month pressure ulcer incidence rate was 13%. All subjects were at risk for pressure ulcer development according to Braden scores; whereas only 74% were assessed at risk with use of the facility's risk assessment tool. Preventive measures included regular repositioning (87%); 67% were placed on mattress support surfaces. There was no relationship between level of risk (facility risk tool score) and type of prevention used. The total cost of pressure ulcer prevention to the nursing unit was $14,926, representing a mean of $497 per subject, and $5.55 per subject per day.

CONCLUSION

As compared with previous studies, the higher cost of prevention described in this study may be attributed to inadequate linkage of preventive interventions to risk level.

Estimating fish consumption rates for Ontario Amerindians

The routine assessment of human exposure to contaminants requires that exposure via consumption of freshwater fish be considered because many chemicals persist and/or bioaccumulate in fish. Estimates of fish consumption rate were determined for Ontario Amerindians from data on the concentration of mercury in the hair of 4,327 Amerindians residing in 58 reserves across the province, combined with data on mercury concentrations in three commonly consumed species of fish collected from lakes surrounding these reserves. Estimated rates of fish consumption were found to differ between sexes, with males consuming a geometric mean of 19 g of fish per day, while females were estimated to consume a geometric mean of 14 g/day. Fish consumption rate was found to increase with increasing latitude, a surrogate measure of community isolation, and to increase with age. Seasonal variation was also noted, with fish consumption rates being highest during summer months and lowest in winter. These data may provide regulatory agencies with a more statistically representative basis upon which to establish assumptions concerning fish consumption rates for risk assessment purposes. Factors such as the location of the exposed population, age and sex of exposed individuals, and time of year in which an assessment is being conducted, should also be considered as specific situations require.

Cognitive-behavioral therapy for migraine headaches: a minimal-therapist-contact approach versus a clinic-based approach

The efficacy of a clinic-based cognitive-behavioral program for the treatment of common migraine was compared to the same approach using a minimal-therapist-contact format by means of a randomized controlled trial. Forty-eight subjects between 18 and 50 years of age completed the program. Following four weeks of recording headache activity, subjects were randomly assigned to a waiting list control condition or to one of the two treatment conditions. Treatment was followed by four weeks of recording of headache activity immediately posttreatment and again six months later. Multivariate analysis of variance indicated that there was a significant reduction in headache frequency, duration and peak intensity following treatment for both treated groups. These reductions were maintained at six months follow-up. Treatment for the minimal-contact group was significantly more cost-effective than for the clinic group.

Acute toxicity, uptake, and clearance of aminocarb by the aquatic isopod, Caecidolea racovitzai racovitzai

Acute toxicity of aminocarb to the aquatic isopod Caecidolea racovitzai racovitzai was found to be proportional to exposure temperature with the potency of the insecticide increasing 1.3 to 5.2 times when the temperature was increased from 12 to 20 degrees C. The 96-hr LC50 values were determined to be 36.1 and 12.0 mg aminocarb/liter for 12 and 20 degrees C, respectively. Uptake and clearance of aminocarb by C. r. racovitzai were also shown to be proportional to temperature indicating that they may be active processes. Control of clearance may be a function of the rate of metabolism of aminocarb in vivo. Both uptake and clearance were shown to occur in two compartments.