Cause-effect pathway

The impact pathways for human toxicity builds on the combination of an environmental fate factor, a human exposure factor, a human toxicity effect factor, and a toxicity-effect damage factor. The fate factor indicates the distribution and transformation of chemicals in the environment, the exposure factor relates the chemical mass in the environment to human exposure, the effect factor indicates potential human toxicity effects per unit of chemical exposure, and the damage factor finally relates potential effects to damages on human health.

Included are organic chemical substances and metal ions.

Modeling approach

Global or (sub-)continental average characterization factors are modeled based on the assumption of linearity between exposure and human population response.

Value choices

To maintain consistency with other impact categories, a time horizon of 100 years is set for the high level of robustness scenarios.

Not all substances with a carcinogenic ED50 are necessarily carcinogenic to humans. The ‘certain impacts’ scenario only includes the substances with strong evidence of carcinogenicity (IARC category 1, 2A and 2B). The ‘all impacts’ scenario includes all substances for which ED50 information is available (IARC category 1, 2A, 2B, 3 or no classification).

Spatial variability

The default are global average characterization factors for different emission compartments (local scale: indoor and urban air; continental and global scale: rural air, agricultural and natural soil, freshwater and marine water).

In addition, characterization factors are available for 8 continental regions (North America; Latin America; Europe; Africa and Middle East; Central Asia; Southeast Asia; Northern regions; Oceania) and 16 sub-continental regions (Central Asia; Indochina; Northern Australia; Southern Australia and New Zealand; Southern Africa; North, West, East and Central Africa; Argentina+; Brazil+; Central America & Caribbean; USA and Southern Canada; Northern Europe and Northern Canada; Europe; East Indies and Pacific; India+; Eastern China; Japan and Korean Peninsula).

Characterisation factors

The toxicity-related human health characterization factor at damage (endpoint) level, CF [DALY/kg emitted] represents the number of disability-adjusted life years (DALY) per kg of chemical emitted to a given environmental compartment, and is derived as

𝐹𝐹 [kg_{in compartment}/(kg_emitted/d)] is the fate factor relating the chemical mass in a given environmental compartment to the chemical mass emitted per day into any environmental compartment. 𝑋𝐹 [(kg_intake/d)/kg_{in compartment}] is the human exposure factor relating the chemical mass taken in per day by a human population to the chemical mass in a given environmental compartment. Fate factor and human exposure factor can be combined into the population intake fraction, 𝑖𝐹 [kg_intake/kg_emitted], directly relating the chemical mass taken in by a human population to the chemical mass emitted to a given environmental compartment or to the chemical mass applied (in case of exposure to pesticide residues in food crops). 𝐸𝐹 [disease cases/kg_intake] is the human toxicity effect factor relating the likelihood (or potential risk) of developing an adverse health effect expressed as number of cancer or non-cancer disease cases to the chemical mass taken in by a human population. 𝐷𝐹 [DALY/disease case] is the human damage factor relating the number of DALY to the number of cancer or non-cancer disease cases, respectively. Out of 3104 substances included in the USEtox characterization model adapted for LC-Impact, human toxicity characterization factors are available for 18 metal ions and 1255 organic substances (931 with non-zero results and with 324 results that equal zero based on being negatively tested for carcinogenicity effects).