Derivation of whole blood biomonitoring equivalents for lithium for the interpretation of biomonitoring data

A review of Health Canada's progress on human biomonitoring-based risk assessments and the path forward

Since the launch of the Chemicals Management Plan (CMP) in 2006, Health Canada has initiated screening-level risk assessments (RAs) of approximately 4300 priority substances under the Canadian Environmental Protection Act, 1999 (CEPA). With the availability of nationally representative human biomonitoring (HBM) data, over 300 of these substances were assessed using HBM-based RA approaches. Qualitative and quantitative HBM-based RA approaches for the regulatory risk assessment of the general population of Canada were developed to increase the efficiency of screening the potential health risk of CMP priority substances. To support HBM-based RAs, several biomonitoring equivalents (BE) were derived to interpret HBM data. For some CMP substances, Health Canada conducted cumulative risk assessments of chemical mixtures using HBM data as measures of exposure. In 2023, CEPA was amended to include the assessment of populations who may be disproportionately impacted (vulnerable populations) and the cumulative effects of multiple chemicals. Going forward, Health Canada is exploring modern approaches in HBM-based RAs, including biomarkers of effect and non-traditional biomarkers (e.g., hair, nails) to address CEPA amendments. This manuscript will discuss Health Canada's progress in HBM-based RAs, and the possible path forward in using HBM data to strengthen human health risk assessments.

Multi-elemental determination of metals, metalloids and rare earth element concentrations in whole blood from the Canadian Health Measures Survey, 2009-2011

BACKGROUND

As part of Government of Canada's Chemical Management Plan, substances containing aluminum (Al), bismuth (Bi), cerium (Ce), chromium (Cr), germanium (Ge), lanthanum (La), lithium (Li), neodymium (Nd), praseodymium (Pr), tellurium (Te), titanium (Ti) and yttrium (Y) were identified as priorities for risk assessment. Generating exposure estimates from all routes of exposure from multiple sources using a traditional approach for these elements can be challenging. The use of human biomonitoring (HBM) data would allow for direct and more precise assessment of the internal concentrations from all routes and all sources of exposure. There are no Canadian or North American population-level whole blood HBM data for the elements listed above. Therefore, this is the first biomonitoring project carried out to determine the concentrations of these elements from a nationally representative sample of Canadians.

OBJECTIVES

The objective of this study was to generate whole blood concentrations for Al, Bi, Ce, Cr, Ge, La, Li. Nd, Pr, Te, Ti and Y in the Canadian population using biobank samples from the Canadian Health Measures Survey (CHMS) cycle 2 (2009-2011) for use in characterizing exposure in screening assessments and for establishing baseline concentrations to determine how exposures are changing over time.

METHODS

The sample analysis was conducted by ICP-MS. A rigorous quality control and quality assurance process was implemented in order to generate data with high accuracy and precision while measuring low concentrations and minimizing possible inadvertent contamination.

RESULTS

Of the elements analysed, the whole blood concentrations (μg/L) of Al, Ce, Cr, Ge, La, Nd, Pr, Te, Ti and Y in the Canadian population aged 3-79 years were below their respective method reporting limit (MRL). Two elements, Bi and Li were detected in 5 % and 66 % of the Canadian population. The median Li concentration was 0.47 μg/L.

CONCLUSION

The results of this study provide information on concentrations of these elements in the Canadian population which can be utilized to characterize exposure in screening assessments and there by the potential for harm to human health. In addition, this study provides baseline HBM data which can be used as a comparative HBM dataset for other populations with similar exposure patterns.

A toxicological evaluation of lithium orotate

Lithium orotate, the salt of lithium and orotic acid, has been marketed for decades as a supplemental source of lithium with few recorded adverse events. Nonetheless, there have been some concerns in the scientific literature regarding orotic acid, and pharmaceutical lithium salts are known to have a narrow therapeutic window, albeit, at lithium equivalent therapeutic doses 5.5-67 times greater than typically recommended for supplemental lithium orotate. To our knowledge, the potential toxicity of lithium orotate has not been investigated in preclinical studies; thus, we conducted a battery of genetic toxicity tests and an oral repeated-dose toxicity test in order to further explore its safety. Lithium orotate was not mutagenic or clastogenic in bacterial reverse mutation and in vitro mammalian chromosomal aberration tests, respectively, and did not exhibit in vivo genotoxicity in a micronucleus test in mice. In a 28-day, repeated-dose oral toxicity study, rats were administered 0, 100, 200, or 400 mg/kg body weight/day of lithium orotate by gavage. No toxicity or target organs were identified; therefore, a no observed adverse effect level was determined as 400 mg/kg body weight/day. These results are supportive of the lack of a postmarket safety signal from several decades of human consumption.