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Table 3 Default and probabilistic approaches to intra-species adjustment for human variability and consideration of susceptible subgroups

From: Current practice and recommendations for advancing how human variability and susceptibility are considered in chemical risk assessment

Agency

TK Subfactor

TD Subfactor

Total Intra-species AF

Type

Subgroup Consideration

US EPA

√10 ≈ 3

√10 ≈ 3

10-fold

Default

Does not explicitly account for sensitive subgroups.

Cal EPA (OEHHA)

10

√10 ≈ 3

30-fold

Default

Children/infants and genetic TK susceptibility (though does not cover fetal period nor all identified variabilities).

IPCS/WHO

2–4.5a

2.5–10a

3.5–42-folda

Probabilistic

Does not explicitly account for sensitive subgroups; data based primarily on studies in healthy adults.

  1. Intra-species adjustment (sub) factors representing human metabolism (TK) and tissue response (TD) TK/TD variability
  2. a IPCS ranges include median and 95th percentile estimates for target population incidence ranging from 1 to 10% [16]
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Environmental Health

ISSN: 1476-069X