Toxicity pesticide mixtures

Patel Y, Kushwah HS, Kushwah A, et al. 1998b. Effect of chronic pesticides mixture toxicity on some enzymes in rats. Indian Vet J 75 698-700. 

The evaluation assumes that the hazard and possible risk of the defined (top-ten) mixture of chemicals is representative for the hazard and risk of the entire complex mixture. For some mixtures that are relatively easily available (e.g., combustion fumes, food products, pesticide mixtures), this assumption could be validated by comparing the toxicity of the top-ten mixture with the toxicity of the original complex mixture in short-term test. 

Deneer (2000) reviewed acute toxicity in aquatic organisms for about 200 pesticide mixtures with diverse modes of action. He found that combined toxicity in 90% of the cases differed from concentration additivity within a factor of 2. Two large studies on the chronic toxicity of binary pesticide mixtures (Faust et al. 1994 Altenburger et al. 1996) demonstrated that, in most cases (> 60%), the best fit of observed mixture effects was to the concentration addition model. 

Belden et al. (2007) used a 3-step approach to evaluate the relative toxicity and the occurrence pattern of pesticide mixtures in streams draining agricultural watersheds. First, a landscape of interest was identified as the corn-soybean crop setting in the United States. Second, the relative toxicity of mixtures was compared... 

Belden JB, Gilliom RS, Martin JD, Lydy MJ. 2007. Relative toxicity and occurrence patterns of pesticide mixtures in streams draining agricultural watersheds dominated by corn and soybean production. Int Environ Assess Manag 3 90-100. 

Deneer JW. 2000. Toxicity of mixtures of pesticides in aquatic systems. Pest Manage Sci 56 516-520. 

Murty A. 1986. Toxicity of pesticides to fish joint action of pesticide mixtures. Boca Raton (FL) CRC Press. 

Belden JB, Gilliom RJ, Lydy MJ. 2007. How well can we predict the toxicity of pesticide mixtures to aquatic life. Integrated Environ Assess Manage 3 362-372. 

Other effects of toxic chemical mixtures on soil are not predictable. Mixtures of fertilizers and pesticides produce enhanced toxic effects. The additions of urea, superphosphate, and potash enhance the toxicities of carbaryl and carbofuran insecticides to nitrogen-fixing bacteria in soilJ26 Soil co-contaminated with arsenic and DDT does not break down DDT as rapidly as soil contaminated with DDT alone. This results in a persistence of DDT in the environment. I27 ... 

The toxic effects of some pesticide mixtures are additive, particularly when their toxic mechanisms are identical. The additive effects of the organophosphates chlorpyrifos and diazanon were demonstrated in one study. T Another study found the s-triazine herbicides atrazine and cyanazine to show additive toxic effects. Not all mixtures of similar pesticides produce additive effects, however. In one study, mixtures of five organophos-phate pesticides (chlorpyrifos, diazinon, dimethoate, acephate, and malathion) were shown to produce greater than additive effects when administered to laboratory animals. Another article discusses nonsimple additive effects of pyrethroid mixtures. Despite the similarities in their chemical structure, pyrethroids act on multiple sites, and mixtures of these produce different toxic effects. 10 ... 

Amphibian endocrine disruption is of special interest to humans. The estrogen found in the painted turtle is identical to that found circulating in the human bloodstream and the endocrine disruptors that threaten wildlife populations have also been shown to be jeopardizing human reproductionAccordingly, animal studies on endocrine disrupting properties of toxic chemicals are relevant to understanding human responses to these chemicals. Pesticide mixtures have been shown to be powerful endocrine disruptors in numerous other animal studiesJ16 Illustrative examples follow. 

In a study using a human neuroblastoma cell line, mixtures of three different organophosphates (azinphos-methyl, diazanon, and dimethoate), and mixtures of an organic phosphate (pirimiphos-methyl) and a benzim-idizole fungicide (benomyl) showed greater toxicity toward protein synthesis than the individual pesticides. I21 The authors of the study concluded that it is not feasible to predict the toxicities of pesticide mixtures on the basis of the toxicities of the single components. 

All the low level pesticide effects discussed earlier, ensued following exposures to mixtures that contained lipophilic and hydrophilic components. This is consistent with the manner in which pesticides are formulated and applied, that is, as mixtures of products, each of which is composed of lipophilic and hydrophilic components. An exhaustive search of the literature did not produce a single example of low level pesticide activity at concentrations at which the pesticide mixtures exhibited toxicity. 

Although there is nu doubt (hut humans are exposed to low doses of mixtures of pesticides (Caslorina e( at, 2003 Duggan et ai, 2003 Fenskc et al. 2002 Sanchez-Pena et ai, 2004), the question is whether mixtures are more toxic than the sum of the toxicity for each pesticide alone. In the literature describing the toxicity of mixtures of organophosphorus (OP) or carbamate (CM) pesticides, concern is expressed that exposure to mixtures of pesticides may be much more toxic than the toxicity of the individual pesticides. This concern about potentiated toxicity is all the more worrisome because data are lacking on the toxicity of pesticide mixtures, whether OP or CM, at less than lethal dosages. There is such scarcity of data, and the data arc so disparate, that a science-ba.scd conclusion on the toxicity of OP or CM pesticide mixtures is not possible,... 

Macck, K. J. (1975). Acute toxicity of pesticide mixtures to blucgills. Bull. Environ. Contam. Toxical 14,648-652. 

The toxic effects of some pesticide mixtures are additive, particularly when their toxic mechanisms are identical. The additive effects of the organophosphates, such as chlorpyrifos and diazinon, were demonstrated in one study [7]. Another study... 

---