Chronic health effects in people exposed to arsenic via the drinking water: dose–response relationships in review

Abstract

Chronic arsenic (As) poisoning has become a worldwide public health issue. Most human As exposure occurs from consumption of drinking water containing high amounts of inorganic As (iAs). In this paper, epidemiological studies conducted on the dose–response relationships between iAs exposure via the drinking water and related adverse health effects are reviewed. Before the review, the methods for evaluation of the individual As exposure are summarized and classified into two types, that is, the methods depending on As concentration of the drinking water and the methods depending on biological monitoring for As exposure; certain methods may be applied as optimum As exposure indexes to study dose–response relationship based on various As exposure situation. Chronic effects of iAs exposure via drinking water include skin lesions, neurological effects, hypertension, peripheral vascular disease, cardiovascular disease, respiratory disease, diabetes mellitus, and malignancies including skin cancer. The skin is quite sensitive to arsenic, and skin lesions are some of the most common and earliest nonmalignant effects related to chronic As exposure. The increase of prevalence in the skin lesions has been observed even at the exposure levels in the range of 0.005–0.01 mg/l As in drinking waters. Skin, lung, bladder, kidney, liver, and uterus are considered as sites As-induced malignancies, and the skin is though to be perhaps the most sensitive site. Prospective studies in large area of endemic As poisoning, like Bangladesh or China, where the rate of malignancies is expected to increase within the next several decades, will help to clarify the dose–response relationship between As exposure levels and adverse health effects with enhanced accuracy.

Introduction

Arsenic (As) is a common element and there are several chances in which people are exposed to As in daily life. Occupational As exposures are observed frequently in smelter workers from the inhalation of As fumes, since As is found as sulfide compounds in various ores as ubiquitous contaminant. Lung cancer is well known to result from As exposure in occupational settings. In recent times, As has become an essential component in the production of semiconductor chips. In occupational settings, workers are often monitored for As exposure level by measuring As contents in biological samples, such as hair, urine, or blood, to help reduce exposure before the onset of the overt clinical manifestations of As poisoning Peyster and Silvers, 1995, Yamauchi et al., 1989. Preclinical manifestations of As exposure can be combined with biological monitoring for As exposure, as with workers engaged in semiconductor industries where hair level of As has been evaluated alone with immunological alternations induced by As exposure (Yoshida et al., 1987). The target population of occupational exposure to As differs from that of general population, because occupational exposure subjects are typically healthy adults with a disproportional distribution of males. In addition, there are often coexisting exposures in occupational settings. Thus, it can be difficult to relate the adverse health effects observed in occupationally exposed workers exclusively to As. Inorganic As (iAs) has been used pharmacologically for the treatment of malaria, syphilis, leukemia, or psoriasis under the name of Fowler's solution, etc. Skin lesions, including dermal malignancies, were observed in the patients who were prescribed arsenical medicines. The prevalence of malignancy was correlated with As intake (Cuzick et al., 1992). These various patient populations are similarly not representative of the general population.

Chronic As poisoning in the general population has been widely reported in many areas of the world today. In these situations, As exposure occurs by consumption of drinking water that naturally contains high amount of inorganic forms of As (Smith et al., 2000b). The outbreak of As poisoning in many areas was triggered by the desire to obtain microorganism-free safety drinking water, and often surface water was replaced by underground water obtained by tube wells. Arsenic poisoning via the drinking water affects all the residents who are living in the contaminated field. Thus, accurate evaluation on dose–response relations between As exposure and adverse health effects in a general population could be assessed in the endemic area of high As exposure. The knowledge of dose–response relationships between As exposure and adverse health effects will help in estimation of health risk and prevention of As poisoning in the future among the resident in areas of endemic As poisoning and also among the workers occupationally exposed to As. In this paper, researches conducted on the dose–response relationships between inorganic As (iAs) exposure via the drinking water and adverse health effects are reviewed.