New Metric CHREL Assesses Cumulative Health Risk from Chemical Exposure in Canadian Population

A recent study by Health Canada introduced a new metric called Cumulative Health Risk from Exposure Load (CHREL), which provides insight into the cumulative health risks posed by multiple chemical exposures. This metric is based on data from the Canadian Health Measures Survey (CHMS) and uses Human Biomonitoring Health-Based Guidance Values (HB2GVs) as thresholds to evaluate the potential health risks from chemical exposures in a population. The findings suggest that a significant portion of the Canadian population may be exposed to chemicals at levels potentially above the HB2GVs, raising concerns about cumulative health risks.

Understanding CHREL: A New Approach to Chemical Exposure

CHREL builds on the concept of Exposure Load (EL), which identifies how many chemicals an individual is exposed to at levels above a certain threshold. CHREL takes this further by integrating HB2GVs, which are exposure thresholds derived from toxicological studies, to evaluate the health risks of chemical mixtures.

By applying HB2GVs, the CHREL metric indicates the number of chemicals detected in an individual that exceeds the health-protective guidance values. The study focused on 18 chemicals measured in CHMS cycles 3 and 4 (2012–2013 and 2014–2015), including mercury, benzene, acrylamide and triclosan. These chemicals have been linked to adverse health effects on the liver, nervous system, and cancer risk.

Key Findings: Chemical Exposures in Canada

The CHREL analysis revealed that more than half of the Canadian population had a CHRELTOTAL score of 1 or higher, indicating exposure to one or more chemicals at levels above the health-based thresholds. Certain subgroups were found to be at higher risk:

• Males had significantly higher CHREL scores compared than females.

• Smokers had notably higher CHREL scores than non-smokers, indicating increased exposure to harmful chemicals.

• Younger age groups (12–19 years) had lower CHREL scores compared to older age groups, especially those aged 40–59.

Small segments of the population also showed higher CHRELLIVER and CHRELNERV scores, which assess risks to the liver and nervous system, respectively. For cancer risk, the study introduced CHRELCANC, based on six chemicals linked to cancer endpoints. Most of the population had an estimated CHRELCANC score of 3, indicating potential exposure to multiple chemicals above negligible cancer risk levels.

Chemicals Driving Health Risks

The study identified several key chemicals that contribute significantly to health risks in the Canadian population:

• Inorganic arsenic was the leading contributor to elevated CHREL scores in the population.

• Mercury, acrylamide, benzene and xylenes were also notable contributors to the overall chemical burden.

• For smokers, the most critical chemicals were inorganic arsenic, benzene, and cadmium, which drove the higher CHREL scores in this group.

Public Health and Policy Implications

The CHREL metric provides a novel way to assess the cumulative health risks of chemical exposures in a population. This information can help guide risk management and regulatory decisions by identifying chemicals that pose the greatest threats to public health. For instance, reducing exposure to inorganic arsenic and other high-risk chemicals could have a significant impact on reducing overall health risks.

The findings underscore the importance of continued biomonitoring efforts, as well as research on how chemical exposures interact to affect human health. Additionally, the study highlights the need for targeted interventions to reduce chemical exposures in vulnerable subpopulations, such as smokers and the elderly.

Limitations and Future Research

While CHREL provides valuable insights, the study has several limitations. The metric relies on available data for a limited number of chemicals, and further research is needed to expand the range of chemicals analyzed. Additionally, the HB2GVs used in the analysis may vary depending on the methods used to derive them, and more work is needed to standardize these values across different chemicals.

Moreover, CHREL does not indicate the level of exposure for each chemical, only whether the exposure exceeds the health-based threshold. As research on chemical interactions and cumulative risk advances, future updates to the CHREL methodology may provide even more refined insights into population-level chemical exposures.

Conclusion: A Step Toward Better Chemical Risk Management

CHREL represents a significant step forward in understanding the cumulative health risks posed by multiple chemical exposures. By integrating biomonitoring data with health-based guidance values, CHREL provides a clearer picture of the chemical exposures of the Canadian population. This metric can serve as a valuable tool for public health officials, researchers, and policy makers to assess and manage the risks associated with chemical exposures, ultimately contributing to improved health outcomes and stronger environmental protection.

The full study can be found here.