State of the Science on Persistent Organic Pollutants

Karluss Thomass, Global Silicone Council

The Society of Environmental Toxicology and Chemistry (SETAC) hosted a side event during the 20th meeting of the United Nations Stockholm Convention on Persistent Organic Pollutants Review Committee (POPRC) from 23–27 September in Rome, Italy.

The Stockholm Convention is a global treaty intended to protect human health and the environment from chemicals that are persistent organic pollutants (POPs). POPs are organic chemicals that have been identified for global action based on the properties of persistence, bioaccumulation and adverse effects, which, when combined with the potential for long-range environmental transport (LRET), can potentially result in significant adverse effects to human health and the environment in remote locations that are distant from sources of their environmental release. Over the last 20 years, there have been notable advancements in the science associated with assessing POPs. These advancements include the development of improved tools aimed at providing a transparent evaluation of the reliability and relevance of various lines of evidence (LoE) that might be used in a weight of evidence (WoE) approach to support the POPRC in its evaluation of whether substances meet the criteria for being identified as POPs under the convention. Utilizing these scientific advancements to support a systematic and transparent data quality evaluation would thus strengthen the adoption of a robust science-based WoE approach, which would greatly benefit the rigor of POPRC assessments and thereby assist the POPRC in fulfilling its obligation to take all information into account.

The event, which was titled “Systematic data quality evaluation and weight of evidence methodology for the assessment of POPs,” built upon previous side events hosted by SETAC during the Stockholm Convention Conference of Parties and POPRC meetings in 2017.

The objectives of the event were to:

• Highlight advancements in the science associated with screening and prioritizing POPs since the Stockholm Convention was ratified.
• Communicate and illustrate how recent (and ongoing) scientific advancements in systematic data quality evaluation and WoE methodology can be utilized within the existing framework of the Stockholm Convention.
• Provide an opportunity to communicate how SETAC can be utilized as a useful resource during POPRC evaluations.

The event featured three speakers including Jon Arnot, University of Toronto; Chris Hughes, Embark Chemical; and Michael McLachlan, Stockholm University. 

Arnot’s presentation, titled “Integrated testing strategies and a weight of evidence approach for bioaccumulation assessment in the Stockholm Convention,” highlighted advancements in the science and interpretation of data for assessing bioaccumulation potential. The presentation noted that the bioconcentration factor (BCF), which is the bioaccumulation criteria for screening bioaccumulative chemicals in the convention, is not aligned with the Stockholm Convention’s goal to protect human and environmental health, is not consistent with the state of the science, and does not take advantage of all the available bioaccumulation assessment methods. For example, years of research have shown that the BCF criteria, which was developed for aquatic organisms, cannot identify all chemicals that can bioaccumulate in air-breathing organisms (e.g., seal, wolf, polar bear). The biomagnification factor (BMF) and trophic magnification factor (TMF) can be used to assess biomagnification, and there has been significant debate as to whether bioaccumulation assessment should only consider BCF in aquatic organisms or biomagnification (e.g., BMFs) in both aquatic and air-breathing organisms. In addition, methods and guidance have been published for collecting, generating and critically evaluating data quality (reliability), and integrating multiple LoE to aid bioaccumulation assessment decision-making following the Organisation for Economic Co-operation and Development (OECD) guidance for a WoE approach. These methods and guidance can improve the ability of the Stockholm Convention to meet its mission and are implemented in two iterative, user-friendly, freely available workflows as the Bioaccumulation Assessment Tool (BAT) and Bioaccumulation Evaluation Tool (BET). The methods are flexible, depending on the user-defined problem formulation (e.g., different bright-line BCF, BAF, BMF criteria, bioaccumulation and/or biomagnification, aquatic organisms and/or air-breathing organisms can be considered). The methods available in the BET and the BAT provide holistic and iterative state of the science knowledge, data and tools for bioaccumulation assessment. When more data are required to establish confidence in a bioaccumulation assessment decisions, these methods provide pragmatic guidance for incrementally addressing uncertainty in the form of an Integrated Approach to Testing and Assessment (IATA) following principles proposed by the OECD.

The presentation by Hughes, titled “Use of systematic data quality evaluation and WoE methodology for assessment of persistence in the Stockholm Convention,” summarized the science associated with the assessment of environmental persistence and the role of the assessment of persistence in the context of a POPs assessment. The environmental persistence of chemicals plays a key role in determining environmental exposure, making it an important consideration for risk assessment and management. Persistence assessments seek to determine the tendency of a chemical to resist degradation processes and remain in the environment after having been emitted. These assessments are inherently challenging because degradation rates in the environment, and in laboratory experiments, can be highly variable due to multiple factors. In addition, certain substance properties can present difficulties in their testing and assessment. These issues, and the fact that a wide variety of relevant information needs to be considered, necessitates that persistence assessments follow a WoE approach. Thus far, detailed guidance on the evaluation of data quality and WoE determination of persistence has been lacking. This can lead to issues of consistency, transparency and robustness in assessments, and it can contribute to contentious decision-making. The presentation discussed these issues and outlined a methodology that has been developed for the systematic evaluation of the reliability and relevance of information and the determination of persistence in accordance with WoE principles. A comprehensive review of relevant test guidelines, regulatory guidance and literature was performed to develop scoring methodologies and rulesets for the evaluation of individual lines of evidence, and to combine lines of evidence to reach persistence assessment conclusions for a chemical.

McLachlan’s presentation, titled “Advancements associated with assessing the potential for long-range environmental transport (LRET),” noted that many chemicals are subject to LRET. Using models, it has been shown that organic chemicals in a large portion of the chemical partitioning space will accumulate in the Arctic following emission to air in temperate latitudes if they are quite persistent. Recently, an assessment of 12,615 high-production-volume chemicals using the OECD overall persistence (Pov) and long range transport potential (LRTP) screening tool showed that 24 percent of these chemicals had an LRET greater than that of existing POPs. This suggests that more sensitive methods and robust techniques will be required to assess the LRET potential of compounds that are nominated as POPs under the Stockholm Convention.

The event was very well received by the POPRC representatives that attended, and there was tremendous enthusiasm all around, ensuring there are future opportunities to engage SETAC in the POPRC process.

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