Adsorption of pyrethroids

Kodaka R, Suzuki Y, Sugano T, Katagi T (2007) Aerobic metabolism and adsorption of pyrethroid insecticide metofluthrin in soil. J Pestic Sci 32 393-401... 

The strong adsorption of pyrethroids for minerals, especially minerals coated with natural organic matter such as are found in soils, is illustrated in our studies by the behaviour of tefluthrin. Thus Figure 9.3 shows sorption of tefluthrin onto organic-free kaolinite, alumina (aluminium oxide) and montmorillonite. Clearly the sorptive capacity of the minerals varies in the order montmorillonite > alumina > kaolinite but all three... 

The adsorption and desorption of pyrethroids to and from soil and sediment are usually described either by the linear or Freundlich isotherm by using the following equations [9] ... 

High hydrophobicity of pyrethroids is likely to result in their bioconcentration in biota which is mostly controlled by lipid content. On the other hand, the high hydrophobicity would reduce bioavailability of pyrethroids due to association with DOM and/or adsorption to suspended and bottom sediments [10]. The bioconcentration factor (BCF) from water to organisms is conveniently defined by... 

Figure 9.2 Adsorption of synthetic pyrethroids onto glass walls in the absence of sorbents (a) permethrin, (b) tefluthrin, (c) cypermethrin and (d) lambdacyhalothrin.

Adsorption column chromatography has been employed to separate the constituents of pyrethrum. Florisil and aluminum oxide have been used as adsorption columns to retain much of the pigmented materials. The pyrethroids may be caused to elute with several solvents. In our experience mixtures of hexane with ethyl acetate, methanol, ethyl ether, dichloromethane, or acetone have provided different elution patterns. 

Figure 9.5, the values obtained in this way vary not only with the extent of natural organic matter coating but also with the character of the OM. This corresponds also to increased adsorption with increased aromaticity of OM. Since the aromaticity of terrestrial-derived (i.e. soil) OM is likely to be high due in part to a preponderance of lignin residues, then soils can be expected to have a high affinity for pyrethroids (Zhou et al., 1994). 

Assuming that pyrethroids may reach estuaries by riverine transport (budgets of this phenomenon are currently being assessed LOIS, 1994) the question arises as to whether re-adsorption onto estuarine particulate matter is possible. Given the findings above, this seems entirely reasonable... 

Despite the high toxicity of fenvalerate and other pyrethroids to aquatic organisms, few environmental problems have been documented, presumably due to the very low application levels needed to control insects, adsorption onto soil and organic matter, and comparatively rapid degradation. Nevertheless, fenvalerate is extremely toxic to aquatic organisms (Table 16.2), has high bioaccumulation, and is persistent in sediments ... 

Two synthetic pyrethroid insecticides, bifenthrin and permethrin (3-phenoxybenzyl (lR5)-cis-fra s-3-(2,2-dichlorovinyl)-2,2-dimcthylcyclopropane-carboxylate), are the major runoff constituents considered in our monitoring and evaluation studies. Bifenthrin has a solubility of <1 ppb, and a Koc of240,000 ml g. Permedirin has a solubility of 6 ppb in water, and a Ka- of 100,000 ml g (5). The stroi adsorption on soil suggests that a large fiaction of the pesticide is associated wifii die suspended solids in nursery runoff. This determines that the downstream distribution of these pesticides is closely related to distribution of sediments, and that practices aiming to remove suspended solids from runoff will also be effective in reducing the level of these pesticides. 

The affinity to glass and PTFE of selected OC, pyrethroid, and triazine pesticides at concentrations <0.25 pg has been described [11]. For the OC pesticides, the adsorption... 

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