Additive toxicity herbicides

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 ... 

The famous herbicide agent orange contained as an additive 2,3,7,8-tetrachlordibenzo-p-dioxin (2,3,7,8-TCDD), the most toxic chemical substance created by mankind. Dioxin makes up about 150-160 kg. in 24,000 tons of herbicide 2,4,5-T. This additive is enough to allow us to continue to discuss the consequences to humans and the environment in Vietnam from not one, but two wars the herbicide and the dioxin [65]. 

Many dioxins were, and still are, introduced into the environment together with phenoxyherbicides - derivatives of 2,4,5-T and 2,4-D. Therefore, the general toxic background created by these herbicides may be much higher than expected, since they can contain many other dioxins as additives along with 2,3,7,8-TCDD. Moreover, these compounds can evolve dioxins when transformed in natural conditions. Thus, the danger of all such pesticides must be measured in two ways by the content of highly toxic dioxins, and by the dioxin precursors [38]. 

Choice of Species. A bewildering variety of exogenous systems have been used for one purpose or another in mutagenicity tests. The choice begins with plant or animal preparations. The attraction of plant systems has stemmed from a desire to avoid the use of animals, where possible, in toxicity testing. In addition, plant systems have particular relevance when certain chemicals are being tested, for example, herbicides. 

That impression gets of a lot of routine reinforcement from news sources. Chemistry is associated with pollution of the atmosphere by ozone and the noxious oxides of nitrogen and sulfur, oil spills, toxic pesticides and herbicides, smelly oil refineries, undesired food additives, chemical accidents, substances of abuse such as heroin, cocaine, and methamphetamine, and chemical weapons. Chemistry gets a lot of bad ink. 

Oxidation of triazine herbicides with chlorine and chlorine dioxide has been widely studied [105-108]. In the case of sulfur-containing triazines, oxidation occurs mainly via cleavage of the weakened R-S-CH3 bond rather than by addition of chlorine. Reactions of S-triazines with chlorine are faster than with chlorine dioxide, and form sulfoxide, sulfone, and a sulfone hydrolysis product. Chlorination with chlorine dioxide only produced sulfoxide [108]. Lopez et al. identified the formation of sulfonate esters during the chlorination of ametryn and terbutryn [106, 107]. Triazine DBFs identified by Brix et al. exhibited higher toxicities than the parent compounds [105]. Similar to triazines, clethodim, a cyclohexanedione herbicide, is oxidized by hypochlorite and chloramines to clethodim sulfoxide and then to sulfone [109]. 

In the utilization of petroleum oils in the field of chemical weed control, oils function as toxicants, as solvents, as filming agents, and as carriers. In view of the very effective synthetic compounds now used as toxicants (substituted phenols), the toxicity of the oils themselves is somewhat less important than it once was. Oils may serve as adjuvants in formulations involving 2,4-D, 2,4,5-T, dinitro compounds, trichloroacetates, and others. They have the unique property of aiding in the contact, spreading, and penetration of herbicides. In addition, synthesis of wetting agents, emulsifiers, and special herbicides may be dependent on petroleum products. 

Quality control standards have been developed for the new petroleum weed killers and laboratory techniques have been worked out tor testing and establishing the suitability of a given petroleum fraction for a specific herbicidal use. Although attempts to correlate herbicidal action with physical and chemical tests have not been entirely successful, the use of additional specific t ts to determine the chemical composition of the fraction has served as an indicator of toxicity in the specific composition under study. 

Exposure assessments characterize the water, diet, and herbicide handling exposure pathways for atrazine and simazine (Sielken et al, 1996, 1998). For each exposure pathway, the chemical-specific doses (mg/kg/day) from each relevant route (ingestion, inhalation, and dermal) are summed. The total chemical-specific dose for each exposure pathway is characterized separately, and then these doses are aggregated by summing over the multiple exposure pathways. The pathway-specific and aggregate assessments are performed separately for atrazine and simazine. In addition, because atrazine and simazine are assumed to have a common mechanism of toxicity, a cumulative exposure assessment is performed combining the doses of atrazine and simazine. 

In addition to the incineration processes, herbicides, CNP (2,4, 6-trichlorophenyl-4 -nitrophenyl ether) and PCP (pentachlorophenol) usage was reported as the major source of dioxins, especially during the late 1960s 1970s. While CNP contained particular non-toxic dioxin congeners such as 1,3,6,8-TeCDD and 1,3,7,9-TeCDD (Yamagishi et al.,... 

Backhaus T, Faust M, Scholze M, Gramatica P, Vighi M, Grimme LH. 2004. Joint algal toxicity of phenylurea herbicides is equally predicted by concentration addition and independent action. Environ Toxicol Chem 23 258-264. 

Herbicides, or weed killers, may be classified as pesticide chemicals. They can kill plants on contact, or they can be translocated (i.e absorbed by one part of the plant and carried to other parts where they exert their primary toxic effect). Most commonly used herbicides have a low toxicity and have caused few adverse effects in users. Some herbicides pose more serious problems to the central nervous system (CNS) and can cause depression. The skin absorption of herbicides also may cause skin irritation, dermatitis, and photosensitization in addition to peripheral motor neuropathies. 

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