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Overview
When evaluating chemical alternatives using the Green Screen for Safer Chemicals methodology, hazard levels must be assigned to the hazard endpoints in order to assign a Benchmark to the chemical. Data availability can vary greatly from endpoint to endpoint and chemical to chemical. In addition, the quality and quantity of data available for a given hazard endpoint and the confidence in the results can vary. The Green Screen methodology is based on the principle that all available data and information should be taken into consideration when evaluating chemicals, and that the best available data be used to support decision-making. The data confidence and quality are visually depicted in the Hazard Summary Table.
Data Preference and Confidence
A weight of evidence approach should be used to assign a hazard level to a given endpoint. Data are preferred in the following order:
Measured data on the specific chemical or listing on an “Authoritative A” list
Measured data from a suitable analog using professional judgment or listing on an “Authoritative B” list
Estimated data from appropriate models or listing on a “Screening” list
The quality of measured data should also be considered in assigning hazard levels based on all available data.
High data confidence is associated with various forms of evidence including valid test data on the chemical or a suitable analog, authoritative lists, and expert judgment that point to the same conclusion. Lower data confidence is associated with data from estimation models, screening lists, inconclusive or conflicted studies and categories of authoritative lists defined by lower data confidence. Hazard levels assigned based on high data confidence are represented with bold text in the Hazard Summary Table. Hazard levels assigned based on low data confidence are represented by italic text in the Hazard Summary Table.
Green Screen Suggested Data Sources
Collecting data on a given chemical can be one of the most time-consuming steps in the Green Screen assessment process. The quality and quantity of data reviewed has a significant impact on the results of the assessment. Effort should be placed on collecting all available data on the given chemical under review, and all valid information located should be considered in the weight of evidence to assign a hazard level to each endpoint. Green Screen recommended data sources are provided [More research required. Can we point to someone else’s guidance or do we need to develop our own?]. The list is not comprehensive, but provides guidance to facilitate data collection. In addition to chemical specific data sources, the Green Screen Supporting Lists provides lists of chemicals that can be used to support the weight of evidence evaluation of the chemical, as described below.
Green Screen Supporting Lists
The Green Screen provides guidance for using available published lists of chemicals to assign hazard levels. The use of such lists reduces resource requirements to conduct an assessment, and promotes consistency of results from multiple reviewers. The lists are divided into three different types, namely authoritative lists, screening lists, and reference lists.
Listing on an authoritative list is based on a comprehensive expert review of the evidence of a specific chemical, and recognized authoritative bodies such as the US EPA publish the lists. Lower confidence is placed in the results of a screening list, either because the review of data is less comprehensive, the review is conducted and/or published by an organization that is not considered a recognized authoritative body, or the list is based predominantly on estimated data or lower confidence data. Reference lists are authoritative or screening lists that can be used to gain information and to flag further review, but cannot be used to assign a specific Green Screen hazard level or benchmark.
A Green Screen hazard level is specified for each category of the authoritative and screening lists (See Green Screen Supporting Lists). Placement in a specific category on an authoritative list is considered high confidence information and the reviewer must assign the specified hazard level (or a hazard level in the specified range) for the given endpoint. In contrast, the hazard level specified for screening lists is a recommended default value. In addition to listing on a screening list, the reviewer may gather additional information and use a weigh of evidence evaluation to assign a hazard level that is different than the recommended level or range. However, the assigned level would require justification, and in the absence of further review the recommended hazard level should be assigned. For more information, see guidance on assigning hazard levels using authoritative and screening lists.
The categories on some specified lists align directly with a specific Green Screen endpoint and hazard level or a specific Green Screen benchmark criterion. For example, GHS Category 1 acute aquatic toxicity criteria align with a Green Screen “very high” hazard level. In such cases a direct translation between the list category and the Green Screen hazard level or benchmark is possible and a single level is specified. These lists are designated as sub-category A (e.g. Authoritative A). For other lists, the list category overlaps with more than one Green Screen hazard level, and a direct translation is not possible. For example, a substance that carries an R23 risk phrase meets the criteria for either “very high” or “high” hazard for acute mammalian toxicity. In such cases, both a default value and the corresponding range of hazard levels are specified. The default value should be assigned, and further research conducted to verify or shift to the appropriate hazard level within the specified range. These lists are designated as sub-category B (e.g. Reference B). The following table summarizes the list types and subcategories.
Please refer to the Green Screen Supporting Lists page and the Green Screen Supporting Lists Reference page for further information.
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