A critical body residue approach for predicting persistent bioaccumulative toxicant effects on reproduction and population dynamics of meiobenthic copepods

Critical body residues (CBRs) are the measured tissue toxicant concentrations yielding a median dose-response on a dry-weight or lipid-normalized basis. They facilitate management decisions for species protection using tissue analysis. Population CBR is the mean dose yielding 50% population suppression and was predicted here in Amphiascus tenuiremis for fipronil sulfide (FS) using lifetables and the Leslie matrix. Microplate bioassays (ASTM E-2317-14) produced biomass sufficient for dry mass and lipid-normalized CBR estimates of reproduction (fertility) and population growth suppression. Significant FS toxic effects were delayed naupliar development (at ≥0.10?μg?L(-1)), delayed copepodite development (at 0.85?μg?L(-1)), decreased reproductive success (at ≥ 0.39?μg?L(-1)), and decreased offspring production (at 0.85?μg?L(-1)). A reproductive median effective concentration (EC50) of 0.16?μg?L(-1) (95% CI: 0.12-0.21?μg?L(-1)) corresponded to an adult all-sex CBR and lipid-normalized CBR of 0.38?pg FS?·?μg(-1) dry weight (95% CI: 0.27-0.52?pg FS?·?μg(-1)) or 2.8?pg FS?·?μg(-1) lipid (95% CI: 2.2-3.6?pg FS?·?μg(-1)), respectively. Copepod log bioconcentration factor (BCF)?=?4.11?±?0.2. Leslie matrix projections regressed against internal dose predicted fewer than five gravid females in a population by the third generation at 0.39 and 0.85?μg FS?·?L(-1) (i.e., 9.6-10.2?μg FS?·?μg(-1) lipid), and 50% population suppression at a CBR of 1.6?pg FS?·?μg(-1) lipid. This more integrative population CBR as a management tool would fall 1.75 times below the CBR for the single most sensitive endpoint-fertility rate.