Pesticide mixture toxicity to algae in agricultural streams – Field observations and laboratory studies with in situ samples and reconstituted water

Long-term pesticide water concentrations were investigated in four agricultural streams and their mixture toxicity on algae was assessed, based realistic (i.e. observed) laboratory tests using (i) natural weekly samples (ii) reconstituted pesticide-spiked representing mixtures with predicted high mixture. This approach both covered the full complexity of controlled samples. monitoring data (time-integrated, samples) revealed more than 11 pesticides (range 11.0 ± 0.25–24.0 0.44) 75% or almost 1600 collected between 2002 2018. ?TUalgae exceeded 0.1 for 29 observations (or 1.8%). Despite multitude a sample, frequently set by one few dominating that contribute to 90% mixture’s toxicity. Algal growth inhibition situ stream showed frequency inhibition, despite low ?TU most these 0.000014–0.3858). These “false positive” results attributed confounding effects turbidity, complexation nutrients, toxic metals and/or other unknown contaminants. spiked significant inhibitory range 1–10x observed worst-case field Although disregard chemical water, they show may occur at monitoring. Furthermore, considering are average likely underestimate short-term peak pesticides, strongly suggest southern Sweden. We conjecture, however, rapid recovery contributes ameliorate contamination should be seen as many stressors drain landscapes.