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Health Assessment of Inorganic Phosphates
Citation:
Petersen, D. Health Assessment of Inorganic Phosphates. SOT 2021 (Virtual), NA, March 12 - 26, 2021.
Impact/Purpose:
Poster Abstract for Scientific Meeting.The Provisional Peer-Reviewed Toxicity Values (PPRTVs) support the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and Resource Conservation and Recovery Act (RCRA). The PPRTV assessments are used by the Superfund program and regional decision-makers to characterize the contamination of a site and when making site-specific clean-up decisions, such as when to pursue monitoring and remediation for a contaminant of concern. The PPRTVs currently represent a tier of human health toxicity values for the EPA Superfund and RCRA hazardous waste programs. Priorities for PPRTV development are based on the needs of the Office of Land and Emergency Management (OLEM) and evaluated annually. PPRTV assessments are derived using accepted, credible and defensible sources of scientific data, methods, and peer-reviewed Agency guidance on dose-response analysis.
Description:
When assessing the human health effects of phosphorus (P), specifically the sodium and potassium salts of inorganic phosphates, there are two notable departures from the traditional risk assessment approach to consider: 1) the background concentrations found in humans is not zero, and 2) the background concentrations found in contaminated sites is not zero. Phosphorus, as commonly found in various phosphates, exhibits a “U-shaped” dose-response curve, where dose levels above deficiency, and dose levels below toxicity, overlap for some population subgroups. Thus, care must be taken in the interpretation of extradietary exposures above a standard American diet that may result from exposures at contaminated sites, and to levels above background, that may be found on those sites. Phosphorus is most commonly found in nature in its pentavalent form in combination with oxygen, known as phosphate or orthophosphate anion (PO43−). Phosphorus is an essential constituent of all living organisms, and its content is quite uniform across most plant and animal species. Data from acute human clinical exposures from bowel preparations show clear renal and gastrointestinal toxicity, but these studies are acute, and may not extrapolate to subchronic or chronic durations germane to human health assessments at contaminated sites. Human dietary studies also show renal, cardiovascular, and skeletal endpoints near the same exposure levels when measured as mg P/kg-d. However, the dosimetry in these studies was determined by dietary surveys, completed years after the exposures, and failed to determine the exact forms of Phosphate in the diet, thus the confidence in the exact dosimetry is low. There is, however, robust animal data from acute, subchronic, chronic and developmental studies in several species, with similar endpoints as in humans. In particular, a subchronic dietary study by Ritskes-Hoitinga et al (2004), which showed nephrocalcinosis in rats and rabbits, under conditions where calcium/phosphate ratios were specified (calcium blocks P absorption) is relevant. Several additional animal studies described similar endpoints at slightly higher doses that further support the relevance of this potential point of departure. Doses that reveled renal effects in humans were similar to doses producing renal effects in humans. Disclaimer: The views represented in this abstract are those of the author and do not necessarily reflect those of the United States Environmental Protection Agency.