A Relative Risk Ranking of Selected Substances on Canada's National Pollutant Release Inventory

ABSTRACT

The National Pollutant Release Inventory (NPRI) provides pollutant release and transfer data from point sources to various media in the Canadian environment. While the inventory serves as Canada's community right-to-know program, the growing number of listed substances and reporting facilities makes it exceedingly difficult for the public to discern which substances are of greatest concern in their respective communities. A chemical's impact is best characterized when its environmental release data are combined with its toxicity and environmental fate properties. Presently, the NPRI does not provide a synthesis of this critical information and there is a need to provide more context with NPRI data to increase its usability. To help deliver this context, a relative risk ranking was compiled for a subset of NPRI substances using a modified Chemical Hazard and Evaluation Management Strategies (CHEMS-1) model. The model combines toxicity, chemical fate properties, and NPRI release data to yield a risk score for each substance. The resulting risk scores are ranked accordingly to provide a priority ranking of the substances. In addition to contextualizing the NPRI release data with hazard information, the ranking can also help set priorities for future risk assessment and evaluation by the Canadian government and scientific community. Limitations included the reliance on modelled data and default values to fill data gaps and uncertain reliability in reported NPRI data. In spite of its limitations, the CHEMS-1 model is a useful tool for prioritizing NPRI substances.

Key Words:

• chemical risk ranking
• chemical scoring
• priority setting
• National Pollutant Release Inventory
• Canadian

ACKNOWLEDGMENTS

A special note of thanks is extended to the staff of Environment Canada's Existing Substance Division. In particular, sincere gratitude goes to Peter Robinson for all his help and cooperation in this work, most notably for sharing data collected in support of DSL categorization, assisting with QSAR selection for aquatic toxicity endpoints, and reviewing an earlier draft of this report. Thanks also go to Mary Swanson, Bill Ernst, Chris Roberts, Pat Doyle, and Christine Garron for reviewing earlier drafts of the report and providing critical feedback.

Notes

¹EPI Suite v3.12 is a collection of quantitative structure–activity relationship (QSAR)–based software that provides estimates for a number of environmental fate properties.

¹ The Existing Substances Division of Environment Canada was tasked with categorizing the 23,000 substances in the DSL by September 2006. Organic and non-metallic inorganic substances were categorized on the basis of persistence, bioaccumulation, and inherent toxicity, whereas inorganic metal- containing substances were categorized based on persistence and inherent toxicity alone.

² The raw data used to compile the risk ranking (including the mean, range, sample size, and associated references) are organized in tabular format in a word file and can be made available on request from the author.

³ Swanson et al. (1997) described two scores in their paper: (1) Not weighted by releases and (2) Weighted by releases. For clarity and simplicity, these terms were renamed hazard and risk score/rank, respectively. This terminology is consistent with a paper by Arnot and Mackay (2008) who refer to a hazard assessment factor (HAF) as a combination of a chemical's persistence (P), bioaccumulation (B), and toxicity (T) and a risk assessment factor (RAF) as a combination of a chemical's P, B, T, and quantity information.

¹wHV_OR = release-weighted HV_OR;

²HV_OR = hazard value for acute rat oral LD₅₀;

³RWF_LW = release weighting factor for land and water releases;

⁴wHV_INH = release-weighted HV_INH;

⁵HV_INH = hazard value for acute rat inhalation LC₅₀;

⁶RWF_A = release weighting factor for air releases;

⁷wHV_CAR = release-weighted HV_CAR;

⁸HV_CAR = hazard value for carcinogenicity rating;

⁹RWF_T = release weighting factor for total releases to all media;

¹⁰wHV_NCAR = release-weighted HV_NCAR;

¹¹HV_NCAR = hazard value for Reference Dose/Concentration;

¹²wHV_AAF = release-weighted HV_AAF;

¹³HV_AAF = hazard value for acute fathead minnow LC₅₀;

¹⁴RWF_W = release weighting factor for water releases;

¹⁵wHV_AAD = release-weighted HV_AAD;

¹⁶HV_AAD = hazard value for acute Daphnia magna EC₅₀.

¹The uncertainty score (ranging from 2–15) indicates the amount of uncertainty associated with a chemical's risk rank. A score of 2 denotes a well-studied substance that has few data gaps whereas an uncertainty score of 15 indicates the substance has limited empirical data and QSARs, expert judgment, and/or default values were used to fulfill many of the model inputs.

¹Estimated by QSAR, surrogate data, or supporting documentation using expert judgment.

²Data requirement fulfilled by default value.