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Time-scale of effects in USEtox

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SandraR
SandraR's picture
Time-scale of effects in USEtox

Hello,

I work with some persistent organic substances, PFOS etc. and wonder about the time-integrated concentration in USEtox. I see that dissociating substances are interrim for example due to the uncertainty in lifespan. But how long time does the substance have effect/expose humans and the environment in the multimedia model? Or is it not time related at all, so that all substances have effect/creates exposure once, independent on the persistency of the substances?

Kind regards,

Sandra

USEtox Team
USEtox Team's picture
Time-scales in USEtox

Thank you for your question.

In the official release version of USEtox, dissociating substances are interim because their fate in the environment is different than that of neutral substances and this aspect is not included in the current model release. In the beta release version, the fate already includes the partitioning behavior for acids and bases.

Furhter, the USEtox model calculates steady-state concentrations in the environment. This is not related to time. For some chemicals, steady-state is reached fast and for others this takes a long time. This is why for example for metals, several LCIA methodologies include specific time horizons, determining concentrations after 20, 100 and 500 or 1000 years. USEtox, however, does not include dynamic calculations. In current LCA it is assumed that an emission related to a product is continuous and a steady-state concentration will therefore "stay". Persistence is included in the fate calculations and concentrations for persistent chemicals will therefore be larger. Subsequently, the exposure and effects are related to the steady state concentrations in the environment.