The effect of confounding variables in studies of lead exposure and IQ.

Methods proposed to address confounding variables frequently do not adequately distinguish confounding from covariation. A confounder is a variable that correlates both with the outcome and the major exposure variable. Accurate treatment of confounding is crucial to low dose extrapolation of the effects of chemical exposures based on epidemiology studies.

Objective ranges of soil-to-dust transfer coefficients for lead-impacted sites.

Residential yard soil and indoor dust datasets from eight communities near historical mining, smelting, and refining operations were used to quantify soil track-in, an important factor in evaluating indoor exposures to soil metals and to set residential soil cleanup levels. Regression analyses were used to derive slopes that represent mass soil-to-dust transfer coefficients or MSDs. Lead concentration data were available for all datasets.

Microplastics in the context of regulation of commercial shellfish aquaculture operations.

Shellfish aquaculture in the Salish Sea (encompassing the Strait of Juan de Fuca, Puget Sound, and the Georgia Strait) is a major source of clams, oysters, and mussels in the United States and Canada. Plastic gear is necessary for the viability of many of these operations. During the past few years, shellfish farm permits issued in Washington State have been challenged on various bases that have included allegations that the plastic gear is releasing microplastics, commonly defined as particles less than 5 mm in diameter.

Assessment of blood lead level declines in an area of historical mining with a holistic remediation and abatement program.

Unlabelled: Lead exposure and blood lead levels (BLLs) in the United States have declined dramatically since the 1970s as many widespread lead uses have been discontinued. Large scale mining and mineral processing represents an additional localized source of potential lead exposure in many historical mining communities, such as Butte, Montana. After 25 years of ongoing remediation efforts and a residential metals abatement program that includes blood lead monitoring of Butte children, examination of blood lead trends offers a unique opportunity to assess the effectiveness of Butte's lead source and exposure reduction measures.

Arsenic relative bioavailability from diet and airborne exposures: Implications for risk assessment.

Major human environmental health concern has been associated with inorganic arsenic (iAs) in drinking water in which dissolved iAs is highly bioavailable. More recently health concerns have been raised regarding the extent of iAs exposure via food and other potential sources. Arsenic relative bioavailability (RBA) in soil is known to be variable; the extent and role of iAs bioavailability in food are not well characterized.

Dermal absorption of arsenic from soils as measured in the rhesus monkey.

Regulatory agencies have relied on dermal absorption data for soluble forms of arsenic as the technical basis for specific absorption values that are used to calculate exposure to arsenic in weathered soil. These evaluations indicate that percutaneous absorption of arsenic from soil ranges from 3.2 to 4.

Percutaneous absorption of arsenic from environmental media.

Current knowledge of percutaneous absorption of arsenic is based on studies of rhesus monkeys using soluble arsenic in aqueous solution, and soluble arsenic mixed with soil (Wester et al., 1993). These studies produced mean dermal absorption rates in the range of 2.

The evolving science of chemical risk assessment for land-applied biosolids.

Biosolids, effluents, and manures are widely applied to agricultural land and other land with varying degrees of pretreatment or control. Regulations governing land application of biosolids take several broad forms in different countries, including limitations based on rates that do not lead to increases in background chemical concentrations or risk assessment approaches such as those used in the United States. Risk assessment is a process that is inherently limited by currently available information and practices, and consequently, risk-based land application limits must be reevaluated periodically.

Risk characterization, assessment, and management of organic pollutants in beneficially used residual products.

A wide array of organic chemicals occur in biosolids and other residuals recycled to land. The extent of our knowledge about the chemicals and the impact on recycling programs varies from high to very low. Two significant challenges in regulating these materials are to accurately determine the concentrations of the organic compounds in residuals and to appropriately estimate the risk that the chemicals present from land application or public distribution.

In vivo percutaneous absorption of arsenic from water and CCA-treated wood residue.

This study was conducted to evaluate the dermal absorption of arsenic from residues present on the surface of wood preserved with chromated copper arsenate (CCA). The research reported herein used methods parallel to those of earlier research on the dermal absorption of radiolabeled arsenic (R. C.

Health effect levels for risk assessment of childhood exposure to arsenic.

Health risks to children from chemicals in soil and consumer products have become a regulatory focus in the U.S. This study reviews short-term health effect levels for arsenic exposure in young children (i.

A market basket survey of inorganic arsenic in food.

Dietary arsenic intake estimates based on surveys of total arsenic concentrations appear to be dominated by intake of the relatively non-toxic, organic arsenic forms found in seafood. Concentrations of inorganic arsenic in food have not been not well characterized. Accurate dietary intake estimates for inorganic arsenic are needed to support studies of arsenic's status as an essential nutrient, and to establish background levels of exposure to inorganic arsenic.

Evaluation of methods for assessing the oral bioavailability of inorganic mercury in soil.

The risks associated with environmental exposures to inorganic mercury are typically assessed based on toxicity studies conducted with the soluble salt, mercuric chloride (HgCl2). Evidence indicates, however, that inorganic mercury is present in soil as a variety of compounds and that oral absorption of inorganic mercury decreases with a decrease in the solubility of the mercury compound being studied. Thus, while HgCl2 is approximately 15-20% bioavailable, the bioavailability of cinnabar (HgS) may be 30- to 60-fold less.

An assessment of lead absorption from soil affected by smelter emissions.

The purpose of this study was to assess the oral bioavailability of lead in soil collected from a former smelter site in Sandy, Utah, USA. Sprague-Dawley rats (approximately 4 weeks of age, 5 of each sex in group) were given either soil lead or lead acetate mixed in a purified diet (AIN-93G ™) at four different concentrations for 31 consecutive days. Food consumption measurements were used to compute mean daily lead exposures for the soil lead and lead acetate groups.

Bioavailability of arsenic in soil and house dust impacted by smelter activities following oral administration in cynomolgus monkeys.

This study was conducted to determine the extent of arsenic (As) absorption from soil and house dust impacted by smelter activities near Anaconda, Montana. Female cynomolgus monkeys were given a single oral administration via gelatin capsules of soil (0.62 mg As/kg body wt) or house dust (0.

Absolute bioavailability of lead acetate and mining waste lead in rats.

The primary purpose of this study was to generate data that could be used to determine the absolute bioavailability of lead using data from a previous study in which soil containing lead from mining waste was mixed with feed. Young male and female Sprague-Dawley rats (7-8 weeks of age, five/sex/group) were given either soluble lead acetate mixed in a purified diet (AIN-76) at three different dose levels (1, 25, and 250 ppm Pb for 30 consecutive days) or intravenously at doses of 0.02, 0.

Use of a five-day test to predict the long-term effects of gastric antisecretory agents on serum gastrin in rats.

It has been hypothesized that prolonged achlorhydria causes compensatory elevation of serum gastrin, and that there is an association in rats between sustained hypergastrinemia, hyperplasia of gastric enterochromaffin-like cells, and subsequent formation of gastric carcinoids in 2-year carcinogenicity studies. The present study examined whether daily administration of gastric antisecretory drugs in rats for 4 days could cause hypergastrinemia associated with inhibition of acid output. Rats were dosed orally for 4 days with the histamine H2-receptor antagonist ranitidine or the H+,K+-sensitive ATPase inhibitor omeprazole, and examined on day 5 for effects on gastric acid secretion and serum gastrin.

Topical application of a tumor promoter induces proliferation of an adherent cell population in murine spleen.

The tumor-promoting phorbol esters have proven to be potent immunomodulatory agents in vitro. It has not been possible to assess the role of phorbol ester-induced alterations of immune function in tumor promotion however, due to a lack of in vivo studies. Studies were therefore designed to assess proliferative responses of murine leukocytes after in vivo exposure to these agents.