Acetone

We purchased chemicals (IMI and CHL; >97.5% purity) from AccuStandard (New Haven, CT, USA) and dissolved them in deionized water (IMI) or acetone (CHL). Pesticide-grade acetone (Fisher Chemical, USA) was used as a solvent carrier for the CHL treatments, and in solvent controls, to a final concentration of 0.01% in exposure water. Our stock solutions were then spiked into control water according to target concentrations, keeping acetone at 0.01%, and mixed thoroughly. Our exposure concentrations matched range-finding experiments and environmentally relevant concentrations (Table S1). In total, D. magna were exposed to six single concentrations (25, 50, 100, 500, 1000, 10,000 ng/L) of each pesticide and three mixture concentrations (25 × 25 ng/L, 500 × 500 ng/L, 10,000 × 10,000 ng/L), a solvent control (for CHL exposures only), and a negative control (control water only). P. promelas were exposed to three single concentrations (25, 500, 10,000 ng/L) of each pesticide and three mixture concentrations (25 × 25 ng/L, 500 × 500 ng/L, 10,000 × 10,000 ng/L), a solvent control, and a negative control. Acute exposure test conditions were identical for both single/binary and field exposures (see Methods Section 2.4.2).