Combined Toxicity of Glyphosate (Faena^®) and Copper to the American Cladoceran Daphnia exilis—A Two-Generation Analysis

Glyphosate and copper are common pollutants in water and soil. Glyphosate is the most used herbicide worldwide; despite being claimed to be a low-toxicity pesticide and easily degraded, several studies have demonstrated glyphosate’s occurrence and toxicity in freshwater ecosystems. Copper is an essential micronutrient; however, at high concentrations, it becomes toxic, and it is a persistent contaminant discharged from agricultural and industrial activities. Both glyphosate and Cu are agrochemicals that can occur in aquatic environments and produce stress in aquatic biota. Cladocerans are important zooplankters, and their sensitivity to chemical stressors has been widely documented. In this study, the North American cladoceran Daphnia exilis was exposed to glyphosate (Faena^®) and Cu mixtures. The effects were assessed in two generations to determine toxicity impairment in the parental (P₁) and filial (F₁) generations. The 48 h median lethal concentration (LC₅₀) of both chemicals was determined. After this, the generations P₁ and F₁ were exposed for 21 days to three concentrations of glyphosate and Cu mixtures (1.04 mg L⁻¹ + 2.45 μg L⁻¹, 1.24 mg L⁻¹ + 3.09 μg L⁻¹, and 1.57 mg L⁻¹ + 4.31 μg L⁻¹), starting from neonates. Survival and reproduction were recorded, and macromolecule content and the size of neonates were measured in the progeny. The LC₅₀ was 4.22 mg L⁻¹ for Faena^® and 13.45 μg L⁻¹ for copper. Exposure to glyphosate and copper reduced fecundity and the number of clutches per female, delayed age at first reproduction, and increased the number of aborted eggs; these effects were more evident in the F₁ than in the P₁. In both generations, the concentration of carbohydrates and lipids was significantly reduced. The treatment and the brood number influenced the total length of neonates, but the total length did not differ significantly, whereas body length and body width decreased in F_1. Glyphosate and copper mixtures significantly increased toxicity in D. exilis in the F₁ generation, probably because the parents produced impaired progenies. Results warn about transgenerational effects in planktonic species chronically exposed to pollutants.