Abstract
This paper compares available options for the
aquatic
ecotoxicological
effect factor component in life cycle assessment (LCA). The
effect
factor is expressed here as the change in risk per unit change in
cumulative exposure, delta Effect/delta Exposure. The comparison
is
restricted to approaches linked, implicitly as well as explicitly, to
species sensitivity distributions (SSDs). This draws on recent
insights for chemical mixtures and identifies the implications of
different model choices. In spite of the many options,
assumptions,
and areas for further research, it is concluded that a single effect
factor basis represents the best available practice for use in LCA at
this time, delta PAFms/delta C = 0.5/HC50; where delta PAFms is the
change in the (Potentially Affected) Fraction (PAF) of species that
experiences an Increase in exposure above a specified effect level,
accounting for the presence of complex background mixtures (ms), delta
C is the change in cumulative exposure concentration of the chemical of
interest, and HC50 is the median, chronic Hazardous Concentration for
regional, multiple species systems. The resultant aquatic effect
factors are risk-based and can be readily estimated for many chemicals
using available methods, without the need to describe the entire SSDs
and without the need for additional data. For example, the
octanol-water partitioning coefficient provides a sufficient estimation
basis for about 50% of existing chemicals that have a narcosis mode of
action. This is also relevant in LCA for more chemicals that are
at
low concentrations in the environment; concentrations below biological
thresholds at which more specific modes of action would be of relevance.
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