Scope and Methodology used in Taking Stock

Data from the three countries' PRTRs were retrieved by the CEC from the three governments or from their publicly accessible websites. The CEC received the data for this year's edition of Taking Stock from Canada in December 2011 and the United States and Mexico in June 2012.

Note: The data sets of the national PRTR systems are constantly evolving as facilities revise previous submissions to correct reporting errors or make other changes.

With the exception of criteria air contaminants (CAC) and greenhouse gases (GHG), all reported data from the three countries are accessible through the TS Online integrated NAPRTR database. CAC are reported to Canada's NPRI and GHG are reported to Mexico's RETC, but these pollutants are not subject to US TRI reporting. However, there are other sources of information on emissions of these pollutants in all three countries, which users can consult for more details: CAC/GHG.

The methodology used in preparation of the annual Taking Stock report and online database includes the following:

• The PRTR data from each country are compiled for the Taking Stock integrated, North American PRTR database. This involves standardizing data fields used in the three countries-for example, aggregating reported off-site transfers to disposal (NPRI) into an "off-site releases" category (see the Glossary).
• Certain individual reported substances are aggregated into pollutant groups or categories (e.g., lead and its compounds, xylene isomers). In these cases, no specific CAS number for the pollutant group is assigned.
• The data are submitted to a general review in order to identify inconsistencies or possible errors, which are then communicated to the national PRTR programs. Although the CEC cannot be responsible for erroneous reporting by facilities, the goal of the North American PRTR project is to use the best data possible.
• Data for each reporting year (going back to 2004) are refreshed at least annually-a fact readers are urged to remember, particularly when attempting to use the  data to analyze time trends. Users can visit the national websites to view changes to the data.

Limitations of the PRTR Data

Because of national PRTR reporting requirements (see Overview of PRTR Reporting Requirements), including thresholds for pollutants and facilities, only a portion of all industrial pollution is being captured. Also, industrial facilities are not the only sources of pollution in North America.

North American PRTR data do not provide information on:

• All potentially harmful substances. The data provide information only on the pollutants reported to each country's PRTR.
• All sources of contaminants. The report includes only those facilities in the countries' industrial sectors, or undertaking specific industrial activities, that are subject to reporting to each national PRTR program. The North American PRTRs do not include emissions from automobiles or other mobile sources, from natural sources such as forest fires or from agricultural sources. For some pollutants, these mobile, natural and agricultural sources can be large contributors to the overall amounts.
• Releases and transfers of all pollutants from a facility. Only those pollutants for which reporting thresholds are met are included.
• All facilities within required reporting sectors. In Canada and the United States, only facilities with the equivalent of 10 full-time employees must report (with certain exceptions). Mexico has no employee threshold.
• Environmental fate of or risks from the pollutants released or transferred.
• Levels of exposure of human or ecological populations to the pollutants.
• Legal limits of a pollutant from a facility. The data do not indicate whether a facility is in compliance with permits and other regulations.

Substances released or transferred by industrial facilities have physical and chemical characteristics that influence their ultimate disposition and consequences for human and ecological health. Assessing the potential harm from particular releases of a pollutant to the environment is a complex task because the potential of a substance to cause harm arises from various factors, including its inherent toxicity and the nature of the exposure to the substance (e.g., the potential risk posed by asbestos sent to a secure landfill is considered to be much lower than the risk posed by asbestos released to air). 

PRTR data alone cannot provide enough information to assess the potential harm from a pollutant; however, the data in combination with other information about a pollutant can serve as a starting point for learning more about its potential impacts. Readers may with to other sources for more information, including:

• ToxFAQs, US Agency for Toxic Substances and Disease Registry
• State of New Jersey, Department of Health, Right-to-Know Hazardous Substances Fact Sheets (information also available in Spanish)