美国环境保护署正在评估目前砷的最大污染水平（MCL）是否足够。如果最近对慢性影响和癌症风险的理论估计被证明是准确的，那么目前的MCL可能无法有效地保护健康。然而，关于砷在人体内的药代动力学和机制的知识还不足以提供一个明确的答案，而且目前的流行病学证据太不一致，关于砷暴露的不确定性太多，无法帮助评估低水平风险。包括85个参考文献、表格和图表。

The adequacy of the current maximum contaminant level (MCL) for arsenic is being evaluated by the US Environmental Protection Agency. If recent theoretical estimates of chronic effects and cancer risks prove accurate, the current MCL may not effectively protect health. Knowledge of arsenic pharmacokinetics and mechanisms in humans, however, is not complete enough to provide a definitive answer, and current epidemiologic evidence is too inconsistent and too fraught with uncertainty regarding arsenic exposure to be helpful in assessing low-level risks. Includes 85 references, tables, figures.