Application of the Biological Toxicity Effect Ratio (BER) Method for Advancing Water Quality Criteria Derivation

Water quality criteria (WQC) serve
as a scientific foundation for
pollutant risk assessment and control in aquatic ecosystems. The development
of regionally differentiated WQC tailored to specific regional characteristics
has become an emerging trend. However, the current WQC is constrained
by a lack of regional species toxicity data. To address these limitations,
this study proposes the biological toxicity effect ratio (BER) method,
which indirectly reflects the toxicity sensitivity of the overall
aquatic ecosystem through the toxicity information on a limited number
of species, enabling rapid WQC prediction. Using the established WQC
in China and the USA as a case study, we combined mathematical derivation
and data validation to evaluate the BER method. Among various species-taxon
groups of freshwater organisms, planktonic crustaceans demonstrated
the highest predictive accuracy. Our analysis further revealed that
species toxicity sensitivity and regional variability jointly influence
the prediction accuracy. Regardless of the evaluation indexes, planktonic
crustaceans emerged as the most suitable species-taxon group for the
BER method. Additionally, the BER method is particularly applicable
to pollutants with conserved mechanisms across species. This study
systematically explores the feasibility of using the BER method and
offers new insights for deriving regionally differentiated WQC.