Organophosphorous insecticides as herbicide synergists on the green algae Pseudokirchneriella subcapitata and the aquatic plant Lemna minor

Abstract

Models proposed for risk assessment of chemical mixtures assume no interactions between the chemicals. There are, however, studies indicating that some organophosporous insecticides can inhibit the detoxification of other chemicals in plants thereby enhancing their effect. The present study investigates whether interactions between selected organophosporous insecticides and herbicides can take place in the aquatic algae Pseudokirchneriella subcapitata and the aquatic macrophyte Lemna minor. For both species binary mixtures of the organophosphate insecticides: malathion, endosulfan and chlorpyrifos were tested together with the herbicides metsulfuron-methyl, terbutylazine and bentazone. For mixtures with malathion on algae, dose-response surfaces were made and the results tested against the model of concentration addition (CA) and independent action (IA). The Lemna minor tests showed no indication of synergy for any of the combinations, on the contrary, significant antagonism was found for several of the mixtures. The response surface analysis showed antagonism in relation to both concentration addition and independent action for mixtures between malathion and metsulfuron-methyl and terbuthylazine, while the mixtures with bentazone could be explained with CA. The study shows no indications of synergistic interactions between the tested pesticides, confirming the applicability of CA as a reference model predicting mixture effects of pesticides for aquatic plants and algae.

Joint toxicity of three plant protection products to Triticum aestivum (L.) and Brassica rapa (L.)

“…A significantly lower toxicity than expected was also observed in a mixture of glyphosate and the organophosphorous insecticide chlorpyrifos applied at field recommended doses to B. napus (Martin and Ronco 2006). Antagonism was also detected in a work dealing with the joint effects of organophosphorous insecticides and herbicides on the green algae Pseudokirchneriella subcapitata and aquatic plant Lemna minor (Munkegaard et al 2008). In the work previously cited, it was concluded that the majority of mixtures tested resulted in antagonism, and no synergism was registered.…”

“…Organophosphorous insecticides, like dimethoate, are known to inhibit the cytochrome P450 in terrestrial plants (Biediger et al 1992) which is known to play an important role in detoxification processes of several xenobiotics in plants (Munkegaard et al 2008). It also has been described that glyphosate inhibits the cytochrome P450 enzyme of wheat plants, which will increase the proportion of toxic molecules reaching the target site (Xiang et al 2005).…”

Assessment of water quality in the Alqueva Reservoir (Portugal) using bioassays

“…It is known that mixtures of pesticides can provoke higher than expected impairment (synergism); so that this is one of the hypotheses raised here. Organophosphorous (OP) insecticides, like CPF, have been reported as plant cytochrome P450 monooxigenases inhibitors in terrestrial plants (Munkegaard et al 2008). Cytochrome P450 monooxigenases are known to play a role in the detoxification processes of xenobiotics and degrading pesticides in higher plants, so it is likely that the degradation of xenobiotics follow similar paths in algae (Munkegaard et al 2008) and a potential inhibition of P450 by OP insecticides in algae could increase its sensitivity to herbicide exposure.…”

New Concept for Evaluating Toxicity of Herbicide for Ecological Risk Assessment

“…A small number of studies have reported the potential threat to macrophytes exposed to pesticide mixtures in aquatic model ecosystems (Fairchild et al, 1994;Lytle & Lytle, 2002Wendt-Rasch et al, 2004). Recent laboratory studies with the standard OECD plant species Lemna minor addressed the joint toxicity of pesticides by applying the two common models of mixture toxicity: concentration addition (CA) and independent action (IA) (Belz et al, 2008;Cedergreen et al, 2007a, b;Munkegaard et al, 2008). The concept of CA is based on the assumption that any component of a mixture can be replaced by another without altering the overall effect of the mixture, and applied for toxicants with similar molecular target sites (Loewe & Muischnek, 1926).…”