Advancing Fifth Percentile Hazard Concentration Estimation Using Toxicity-Normalized Species Sensitivity Distributions

The species sensitivity distribution (SSD) is an internationally
accepted approach to hazard estimation using the probability distribution
of toxicity values that is representative of the sensitivity of a
group of species to a chemical. Application of SSDs in ecological
risk assessment has been limited by insufficient taxonomic diversity
of species to estimate a statistically robust fifth percentile hazard
concentration (HC5). We used the toxicity-normalized SSD (SSDn) approach,
(Lambert, F. N.; Raimondo, S.; Barron, M. G. Environ. Sci.
Technol.2022,56, 8278–8289),
modified to include all possible normalizing species, to estimate
HC5 values for acute toxicity data for groups of carbamate and organophosphorous
insecticides. We computed mean and variance of single chemical HC5
values for each chemical using leave-one-out (LOO) variance estimation
and compared them to SSDn and conventionally estimated HC5 values.
SSDn-estimated HC5 values showed low uncertainty and high accuracy
compared to single-chemical SSDs when including all possible combinations
of normalizing species within the chemical-taxa grouping (carbamate-all
species, carbamate-fish, organophosphate-fish, and organophosphate-invertebrate).
The SSDn approach is recommended for estimating HC5 values for compounds
with insufficient species diversity for HC5 computation or high uncertainty
in estimated single-chemical HC5 values. Furthermore, the LOO variance
approach provides SSD practitioners with a simple computational method
to estimate confidence intervals around an HC5 estimate that is nearly
identical to the conventionally estimated HC5.

物种敏感性分布（species sensitivity distribution, SSD）是国际公认的基于毒性值概率分布开展危害估算的方法，该分布可表征某类物种对某一化学物质的敏感性。此前，SSD在生态风险评估中的应用受限于物种分类学多样性不足，难以通过统计方法得到稳健的5%危害浓度（fifth percentile hazard concentration, HC5）。本研究采用毒性归一化SSD（toxicity-normalized SSD, SSDn）方法（Lambert, F. N.; Raimondo, S.; Barron, M. G. *Environ. Sci. Technol.*, 2022, 56, 8278–8289），并对其进行改进以纳入所有可用于归一化的物种，以此估算氨基甲酸酯类与有机磷杀虫剂类化合物的急性毒性数据对应的HC5值。我们采用留一法（leave-one-out, LOO）方差估计，计算了每种单种化学品的HC5值的均值与方差，并将其与SSDn法及传统方法估算的HC5值进行对比。当在化学品-类群分组（氨基甲酸酯类-所有物种、氨基甲酸酯类-鱼类、有机磷类-鱼类、有机磷类-无脊椎动物）内纳入所有归一化物种组合时，SSDn法估算的HC5值相较于单化学品SSD法，不确定性更低且准确性更高。对于物种多样性不足以计算HC5值，或单化学品HC5估算不确定性较高的化合物，推荐采用SSDn法估算其HC5值。此外，留一法方差估计可为SSD应用者提供一种简便的计算方法，用以估算HC5估算值的置信区间，其结果与传统方法估算的HC5置信区间几乎一致。