Add a qualifier for hazardous classifications

[eKathleenCarter]

Is your feature request related to a problem? Please describe.
I want to represent standardized hazard classifications (GHS categories, EPA toxicity categories, etc.) in chemical toxicity associations. Currently, there is no appropriate Biolink qualifier (or other slot) to capture regulatory hazard classifications like "GHS acute toxicity category 4" or "EPA toxicity category III" when modeling chemical-to-phenotype associations.

What working group (or team) did this request originate from?
N/A

Note: This is relevant for members of NCATS Translator.

Describe the solution you'd like

hazard_classification_qualifier:
  is_a: qualifier
  description: >-
    A qualifier that specifies the hazard classification assigned to a 
    chemical substance based on standardized regulatory frameworks 
    such as GHS, EPA, or other established classification systems.
  domain: association
  range: string
  examples:
    - value: "GHS_acute_toxicity_category_4"
    - value: "EPA_toxicity_category_III"
    - value: "GHS_carcinogenicity_category_1B"
  notes:
    - "Used for standardized hazard classifications from regulatory frameworks"
    - "Common frameworks include GHS, EPA, IARC, EU CLP"

Additional information to support this request (optional)

• Use case: Chemical toxicity databases commonly includes both quantitative measurements (LD50 values) or standardized classifications (GHS categories, EPA categories)
• Data example: A chemical might have "LD50 > 5000 mg/kg" (quantitative) or "GHS acute toxicity category 5" (classification) in the oral toxicity data set
• https://ice.ntp.niehs.nih.gov/DATASETDESCRIPTION
• Current gap: Quantitative data fits in has_attribute with QuantityValue, but regulatory classifications have no appropriate qualifier (or attribute)
• Semantic distinction: These are standardized regulatory classifications, not clinical modifiers, severity ratings, or other existing qualifier types
• International relevance: GHS is globally harmonized, EPA categories are US-specific, EU CLP is European - this qualifier would support international chemical safety data integration
• ROBOKOP integration need: This qualifier is essential for properly ingesting ICE (Integrated Chemical Environment) toxicity data into ROBOKOP. Without it, we cannot accurately represent the regulatory classification information that is a key component of chemical hazard assessment data in the ICE database.

Tag relevant members for discussion
@cbizon @karafecho @sierra-moxon @EvanDietzMorris

[eKathleenCarter]

I am also open to other ideas for modeling thse classifications.

[eKathleenCarter]

From @karafecho

Thanks, Kathleen. Just a thought, but do we want to suggest has_attribute with ClassificationValue, if only for consistency with quantitative metrics?