Inorganic arsenic: a need and an opportunity to improve risk assessment.

This paper presents views on the current status of (inorganic) arsenic risk assessment in the United States and recommends research needed to set standards for drinking water. The opinions are those of the Arsenic Task Force of the Society for Environmental Geochemistry and Health, which has met periodically since 1991 to study issues related to arsenic risk assessment and has held workshops and international conferences on arsenic. The topic of this paper is made timely by current scientific interest in exposure to and adverse health effects of arsenic in the United States and passage of the Safe Drinking Water Act Amendment of 1996, which has provisions for a research program on arsenic and a schedule mandating the EPA to revise the maximum contaminant level of arsenic in drinking water by the year 2001. Our central premise and recommendations are straightforward: the risk of adverse health effects associated with arsenic in drinking water is unknown for low arsenic concentrations found in the United States, such as at the current interim maximum contaminant level of 50 microg/l and below. Arsenic-related research should be directed at answering that question. New epidemiological studies are needed to provide data for reliable dose-response assessments of arsenic and for skin cancer, bladder cancer, or other endpoints to be used by the EPA for regulation. Further toxicological research, along with the observational data from epidemiology, is needed to determine if the dose-response relationship at low levels is more consistent with the current assumption of low-dose linearity or the existence of a practical threshold. Other recommendations include adding foodborne arsenic to the calculation of total arsenic intake, calculation of total arsenic intake, and encouraging cooperative research within the United States and between the United States and affected countries.

Indoor air radon.

This review concerns primarily the health effects that result from indoor air exposure to radon gas and its progeny. Radon enters homes mainly from the soil through cracks in the foundation and other holes to the geologic deposits beneath these structures. Once inside the home the gas decays (half-life 3.8 d) and the ionized atoms adsorb to dust particles and are inhaled. These particles lodge in the lung and can cause lung cancer. The introduction to this review gives some background properties of radon and its progeny that are important to understanding this public health problem as well as a discussion of the units used to describe its concentrations. The data describing the health effects of inhaled radon and its progeny come both from epidemiological and animal studies. The estimates of risk from these two data bases are consistent within a factor of two. The epidemiological studies are primarily for hard rock miners, although some data exist for environmental exposures. The most complete studies are those of the US, Canadian, and Czechoslovakian uranium miners. Although all studies have some deficiencies, those of major importance include uranium miners in Saskatchewan, Canada, Swedish iron miners, and Newfoundland fluorspar miners. These six studies provide varying degrees of detail in the form of dose-response curves. Other epidemiological studies that do not provide quantitative dose-response information, but are useful in describing the health effects, include coal, iron ore and tin miners in the UK, iron ore miners in the Grangesburg and Kiruna, Sweden, metal miners in the US, Navajo uranium miners in the US, Norwegian niobian and magnitite miners, South African gold and uranium miners, French uranium miners, zinc-lead miners in Sweden and a variety of small studies of environmental exposure. An analysis of the epidemiological studies reveals a variety of interpretation problem areas. The major and almost universal problem is in estimating exposure levels. In many cases there were no direct measurements of radon or radon progeny and the exposure levels are estimates based on irregular measurements and known levels in nearby mines. Perhaps the most important variable or complicating factor in the determination of the risk due to radon exposure is the confounding factor of exposure to cigarette smoke. The general scientific concensus is that, although the interaction could be somewhere between linear and supramultiplicative, it is likely a combination, and closer to multiplicative. A number of other complexities contribute to the uncertainty in the risk estimates, likely to a lesser degree than those of exposure measurements and cigarette smoke confounding.(ABSTRACT TRUNCATED AT 400 WORDS)

Some scientific judgments in the assessment of the risk of environmental contaminants.

The assessment of risk due to environmental contaminants depends, in part, on scientific data. When such data are incomplete, as is usually the case, assumptions based on scientific judgments are made to analyze the consequences. Specifically, when health related data needed to assess the risk posed by environmental contaminants are missing or incomplete, it becomes necessary to make assumptions using scientific judgment to estimate the risk. Different scientists can and do make different assumptions, and the resulting differences in opinion can result in controversy. The present discussion presents a few of the consensus judgments of the Science Advisory Board (SAB) of the U.S. Environmental Protection Agency concerning the health effects and risk for such environmental contaminants as 1,2-dichloroethylene, dichloromethane, para-dichlorobenzene, polychlorinated biphenyls, perchloroethylene, and xylene, as well as the implications of the more likely cancer mechanisms, the exposure routes, and pharmacokinetics to the risk assessment process. In some of these examples, the scientific data have been developed to the extent that specific judgments by groups such as the SAB can result in greater confidence that one is correct in the assessment of risk. Because of the uncertainties in current scientific knowledge for many environmental contaminants, judgments differ and there is no right or wrong opinion.

Naturally occurring radionuclides in drinking water: An exercise in risk benefit analysis.

The scientific background information describing the occurrence, measurement, health effects, treatment technology, risk assessment and economic consequences of the presence of naturally occurring radionuclides in drinking water are described for 60,000 public drinking water supplies. The relevant data for the occurrence of radium, uranium and radon in drinking water supplies are discussed and analysed. Radon is of importance because it is released in the process of taking showers and baths and in washing dishes and clothes. Its progeny is then inhaled, leading to the risk of lung cancer. Radium and uranium can both cause bone cancer. The range of average occurrence of natural radioactivity in drinking water is as follows:(226)Ra, 0.3 to 0.8 pCi L(-1);(228)Ra, 0.4 to 1.0 pCi L(-1); uranium, 0.3 to 2.0 pCi L(-1) and(222)Rn, 500 to 600 pCi L(-1). The estimated lifetime risks due to the mean groundwater concentrations of naturally occurring radionuclides are:(226)Ra and(228Ra), 1.0 10(-5); uranium, 2.0 × 10(-6) and radon, 4.0 × 10(-4). The cost to reduce total radium levels to 5.0 pCi L(-1) is about $9 million. An equivalent expenditure would be required to reduce radon levels to about 4,000 pCi L(-1), or uranium levels to about 100 pCi L(-1). The problem of maximizing the total mortality and the reduction per unit dollar outlay per unit dollar cost for the uranium/radon case is examined.

A Bayesian analysis or scientific judgment of uncertainties in estimating risk due to 222Rn in U.S. public drinking water supplies.

The elements which contribute to the range of values or uncertainties for the lifetime risk and dose equivalent due to 222Rn in U.S. public drinking water supplies are estimated and discussed here. From imperfect scientific knowledge, reasonable upper and lower bounds are placed on these estimates through the use of a semiquantitative Bayesian approach to uncertainty analysis. The factors considered are: occurrence of 222Rn in drinking water, indoor air 222Rn concentrations as a function of drinking water concentration, equilibrium state of the progeny, fraction of daughter products attached to aerosol particles, anatomical and dosimetric variables, epidemiological studies and choice of latency period, plateau period and effects of age. For Rn in U.S. public drinking water supplies, it is estimated that the best estimate for the lifetime lung cancer risk factor is 5 X 10(-9) excess cases of lung cancer per becquerel of Rn per m3 of water (2 X 10(-7) excess cases of lung cancer per picocurie of Rn per liter of water), with an estimated range between 2 X 10(-9) and 2 X 10(-8) excess cases per becquerel of Rn per m3 of water (5 X 10(-8) and 7 X 10(-7) excess cases per picocurie of Rn per liter). The best estimate of the lifetime population risk due to 222Rn in U.S. public drinking water supplies is estimated to be 6,000 excess lung cancers, with a reasonable range of 1,000 to 30,000.

Predicting the occurrence of 228Ra in ground water.

A conceptual model is presented to predict the relative probability of the occurrence of elevated 228Ra in public drinking water supplies (those which serve more than 25 people or 15 connections) using ground water sources. The model is based on an aquifer classification scheme, which is developed from an understanding of the geochemical and radiological behavior of 228Ra and its parent, 232Th. Using this model, all aquifer types are classified as low, medium, or high probability of having elevated 228Ra. Summaries of the available data are discussed to show the actual concentrations found in each type of aquifer. As part of the initial application of this approach to develop a nationwide occurrence profile for 228Ra, all counties in the United States were classified and a map presented to show the distribution of the three classes. Nationwide, 71% of the counties were ranked as low, 18% were ranked as medium, and 11% were ranked as high.

Drinking-water contribution to natural background radiation.

The average concentrations of naturally occurring radionuclides in drinking water are estimated from recent measurements and are used to estimate the annual effective dose equivalent associated with drinking water due to the different radionuclides. The annual effective dose equivalents are determined from the annual intake of these radionuclides using dosimetric information based on ICRP Publication 30 dosimetric models and cohort analysis considering risk coefficients developed by the U.S. Environmental Protection Agency using data from the report of the Biological Effects of Ionizing Radiation Committee (BEIR III) of the National Academy of Sciences. The resulting contribution from drinking water sources to the annual effective dose equivalent is in the range of 0.002 to 0.05 mSv/y (0.2-5 mrem/yr) for those using community drinking water supplies (approximately 216 million people in the United States). The contribution to the annual effective dose equivalent from 222Rn dissolved in water is in the range of 0.8-30 mu Sv/y (0.08-3 mrem/yr) based on the inhalation pathway following the release of 222Rn from drinking water.

Regulatory development of the interim and revised regulations for radioactivity in drinking water--past and present issues and problems.

Developing the Revised Regulations for Radioactivity in Drinking Water under the Safe Drinking Water Act requires information from all related areas and disciplines. As one step in the regulatory process, the background and history of that process as it applies to radioactivity in drinking water is described. The issues involved in developing the revised regulations are as follows: monitoring and sources of exposure, dose evaluation, health effects, engineering, economics and general policy development.

Estimating risk for carcinogenic environmental contaminants and its impact on regulatory decision making.

Increasingly risk analysis and risk estimation are important tools used in regulatory decision making. To appreciate the complexities of this multifaceted field and gain some understanding of it, a broad overview is the first step. This paper attempts to do this. The view is admittedly imperfect and incomplete, but should help the reader see more clearly many of the features and limitations of risk estimation for environmental contaminants. A scheme is suggested for use of quantitative individual risk rates and population risk rate estimates in regulatory decision making.

Compliance data for the occurrence of radium and gross alpha-particle activity in drinking water supplies in the United States.

Most of the results of the first systematic nationwide monitoring of public water supplies for 226Ra have been received. Approximately 50,000 public water supplies have been sampled of a total of 59,812. It is estimated that once the drinking water from all supplies has been analyzed, approx. 500 samples will exceed the Maximum Contaminant Level (MCL) of 5 pCi/l. Almost all the violations occur for ground water supplies. Monitoring in some states is incomplete but the geographical distribution of these water supplies that exceed the MCL is clear. This study is compared to other information concerning the concentration of 226Ra in drinking water supplies and the implications of this information are discussed.

Occurrence of uranium in drinking water in the U.S.

Uranium is found in ground and surface waters due to its natural occurrence. In some cases, its presence is due to human activities such as mining and milling uranium. Thus, it is also found in drinking water. The range of concentrations existing in drinking water supplies in the U.S. is tabulated and examined. The range of isotopic abundances are also listed. Projections from the available data lead to estimates that of the 59,812 community drinking water supplies in the U.S., 25-650 would exceed a uranium concentration of 20 pCi/l., 100-2000 would exceed 10 pCi/l. and 2500-5000 would exceed 5 pCi/l.

Health effects guidance for uranium in drinking water.

The interim regulations for radioactivity in drinking water were promulgated in 1976 (Federal Register, Friday, 9 July, 1976, p. 28402). These regulations specifically excluded uranium because of uncertainties concerning its toxicology, treatment technology and occurrence. At this time, EPA's Office of Drinking Water is considering proposing a health effects guidance level of 10 pCi/l. (0.37 Bq/l.) for uranium in drinking water. This paper describes the approach that EPAs Office of Drinking Water is considering in developing the guidance level. This value has not yet been officially determined to be EPA's formal guidance, but is presented as a working hypothesis for review and comments. Included here is a discussion of occurrence, pharmacokinetics and health effects. The calculation of doses uses the ICRP 30 model and the risk determination uses EPA's newly developed life table approach. The risk level from ingesting drinking water with a uranium content of 10 pCi/l. is estimated to be about 3 X 10(-5) excess cancers/lifetime.