NRC convened the Committee to Assess the Health Implications of Perchlorate Ingestion, which prepared this report.
In 1985, the Region 9 Office of EPA raised concern about potential perchlorate contamination at Superfund sites in the San Gabriel Valley in California (see Figure 1-1 for timeline of selected perchlorate-related regulatory activities) (Takata 1985). No validated analytic method was available to measure low perchlorate concentrations, and little information on their possible health effects was available (EPA 2002a). As a result, attention was focused on other chemicals at the California sites.
In the early 1990s, perchlorate contamination in monitoring wells at a California Superfund site was confirmed at concentrations greater than 1 part per million (ppm) (1 milligram per liter [mg/L]), and a provisional RfD was issued by the EPA Superfund Technical Support Center in 1992 (EPA 2002a). A revised provisional RfD was released in 1995. The RfDs were considered provisional because they had not undergone internal or external peer review. However, they were used to derive guidance levels for groundwater remediation (see Table 1-1).
In March 1997, Toxicology Excellence for Risk Assessment (TERA), a nonprofit risk assessment consulting firm, convened an independent peer review to evaluate an RfD that it had derived for perchlorate (EPA 2002a). The peer review concluded that the scientific database was insufficient to conduct a “credible quantitative risk analysis.” As a result, an independent peer-review panel met in May 1997 and developed a testing strategy to address data gaps and reduce uncertainties regarding possible health effects of low-concentration perchlorate ingestion. The panel recommended a subchronic oral bioassay in rats, a developmental-neurotoxicity study in rats, a developmental study in rabbits, a two-generation reproductive toxicity study in rats, pharmacokinetic and mechanistic studies in test animals and humans, and genotoxicity and immunotoxicity assays.
In 1998, perchlorate was placed on EPA’s final version of the Contaminant Candidate List (CCL), which names unregulated contaminants that may pose a public-health concern in drinking water (EPA 2004b). Contaminants on the CCL are being considered for regulation; that is, they are not subjects of federal drinking-water standards. To determine the extent of perchlorate contamination of the national drinking-water supply, monitoring of perchlorate in all large public water systems and a representative sample of small systems became mandatory beginning in 2001 (EPA 2004c).