Significant differences of toxicity, bioconcentration and biomagnification effects of surfactants on organisms in the food chain under combined exposure from those under single exposure.

Surfactants, the primary active components in cleaning and disinfection products, are being discharged into the water environment and threatening the health of aquatic organisms. Moreover, the combined exposure of surfactants exacerbates the risks. However, the combined exposure effects such as toxicity, bioconcentration and biomagnification effects of surfactants on the organisms especially those in the food chain remain insufficiently unexplored. Therefore, the combined exposure effects of three surfactants, cetylpyridinium chloride monohydrate (CPC), didodecyldimethyl ammonium bromide (DDAB), and dodecyl dimethyl benzyl ammonium chloride (DDBAC) on organisms in the food chain were investigated. The results showed that surfactants exert toxic effects on C. pyrenoidosa by damaging the photosystem, inhibiting chlorophyll synthesis, and inducing oxidative stress via ROS overproduction. The toxicity order of the three surfactants is CPC > DDBAC > DDAB, which is correlated with protein binding affinity and further confirmed by molecular docking analysis. Surprisingly, the combined toxicity was not a simple sum of three surfactants, but exhibited time- and concentration-dependent synergism and antagonism. Significant bioconcentration of surfactants appears in both species under single (BCFs: 190.81 ± 14.50 ~ 8435.86 ± 139.29 for C. pyrenoidosa; 44.77 ± 2.79 ~ 2939.64 ± 83.08 for Daphnia magna (D. magna)) and combined exposure (BCFs: 222.86 ± 5.25 ~ 6085.32.86 ± 88.98 for C. pyrenoidosa; 70.25 ± 9.40 ~ 2032.83 ± 72.34 for D. magna). During the food chain transfer process, DDAB exhibited a biomagnification effect (BMF > 1) when exposed alone, while all other treatments—whether single or combined—exhibited biodilution. Notably, combined exposure altered the bioaccumulation effect: compared to single exposure, the bioaccumulation potential of CPC and DDBAC increased under combined exposure conditions. In summary, these findings highlight that co-exposure intensifies toxicological effects and nutrient transfer phenomena. Comprehensive risk assessments of surfactants in natural environments must incorporate co-exposure factors.