Biocides permethrin

Biocides most often found in the indoor environment are chlorinated hydrocarbons like chlordane, DDT, dieldrin, lindane, heptachlor and methoxychlor, pyrethroids like cyfluthrin, cypermethrin, and permethrin, organophosphates like chlorpyrifos, diazinon, dichlorvos, isofenfos, and malathion, carbamates like ben-diocarb, carbaryl and propoxur and chlorophenols like pentachlorophenol (PCP), chlorocresol (4-chloro-3-methylphenol) and o-phenylphenol. Residues formed in house dust may vary in different countries (Butte, 2003), but biocides like chlorpyrifos, DDT, methoxychlor, permethrin, pentchlorophenol and propoxur seem to be the active compounds in biocide formulations even in different continents, as they are found equally in house dust samples form Germany and the USA (Becker et al., 2002 Butte, 2003 Camann, Colt and Zuniga, 2002). Concentrations of biocides in house dust are mostly in the milligram per kilogram range, they seldom exceed a microgram per cubic meter in indoor air. 

Concentrations of some biocides in the indoor environment show a tendency to decrease, others increase. According to the German environmental surveys (GerES), performed for nearly 20 years, concentrations of PCP in house dust are declining, a tendency already reported (Butte, 2003). On the other hand concentrations of lindane, piperonylbutoxide and permethrin seem to increase (Becker et al., 2002 Seifert et al., 2000). 

In the past, PCP, lindane and DDT have been used in several instances in Germany to protect wood indoors. In recent years modem biocides such as pyrethroids (e.g. permethrine) or triazoles (e.g. tebuconazole) have been used instead of the classical organic chloro-pesticides to protect wood. 

The latest wood preservatives contain a mixture of different biocides. Normally these are combinations of fungicides and insecticides e.g. dichlofluanid, tebuconazole and permethrine in the concentration range 0.03-1.0 % in solution together with other ingredients such as plasticizers, pigments and others. 

These relatively new biocides have a very low vapor pressure (tebuconazole 1.3 x 10 to 7.2 X 10 Pa, permethrine 1 x lO" to 4.5 x 10 Pa) compared to former biocides (lindane 1.2 x 10 to 9,4 x 10 Pa). Substances such as PCP, lindane or DDT are already found indoors in gaseous form or adsorbed to dust modem biocides such as pyrethroids are only found adsorbed to dust. 

In spite of this observation, extraction of the filters showed nearly the same concentrations for tebuconazole and permethrine as found for sampling with PUF alone (see Table 1.3-1). These results show that for the sampling of biocides with very low vapor pressures (e.g. permethrine and tebuconazole) a quartz filter retains not only particle- or dust-bonded permethrine but also gaseous permethrine. Sampling with a quartz filter in front of the PUF does not allow differentiation between the two. 

The concentration for dichlofluanid decreases with time from about 20 pg/m to less then 1 pg/m. This was the expected lapse, although starting concentration was above the saturation concentration if calculated by vapor pressure (1. 3 X 10- Pa to 1.4 X 10-5 Pa at 20 °C). In contrast to this normal decrease are the curves for permethrine and tebuconazole. At the beginning of the measurements the concentrations were Just detectable. During the first weeks there was a slight increase up to 10 ng/m. Then there was a further increase to about 30 ng/m. After 150 days a slight decrease in the air concentration started. This course of the concentration increase might be explained by sink effects. Because of their low vapor pressure tebuconazole and permethrine are more likely to be adsorbed onto the inside surface of the chamber. Before the air concentration can rise to the steady state concentration the chamber walls must be saturated with the biocides. 

From Table 1.3-3 it can be seen that even over the time period of 862 days (nearly 3 years) less than 1 % of the applied amount of the very low volatile biocides such as tebuconazole and permethrine has been released into the air. In contrast to this the release for dichlofluanid amounts to about 25 %. 

Depending on the volatility of the biocide, some weeks or months after application vaporization will lead to levels not higher than some hundred ng/m for non-volatile biocides such as permethrin, whereas semivolatile compounds such as PCP may be present in concentrations of some pg/m. Concentrations of PCP in indoor air are < 0.025 pg/m (Eckrich, 1989), < 0.05 pg/m (Butte Walker, 1994), respectively, if no wood preservatives have been applied. In our experience, concentrations of PCP in indoor air of rooms where PCP has been used as a wood preservative more than 20 years ago are nowadays in many cases of the same magnitude as in rooms where PCP has never been applied. 

Wood preservatives and agents against insects and fleas are used by more than two-thirds of the population thus their residues can be found in nearly every home. Only in two households (< 1 %) could no biocide or synergist be observed. On the other hand chlorpyriphos, propoxur and lindane were present in more than 10 %, PBO in more than 50 %, DDT, permethrin and methoxychlor in more than two-thirds and PCP in nearly every sample. Results regarding concentrations of biocides in household dust were confirmed by those obtained in Schleswig-Holstein (LANU, 1997), but information about the use of biocides indoors was not obtained for the latter study. 

The biocides most often occurring in household dust in Germany are methoxychlor, PCP and permethrin, Methoxychlor is rarely found in formulations intended for indoor use publications reviewing concentrations in dust are so far not available. However, about 80 % of the dust samples showed residues of more than 0.1 mg/kg and up to several mg/kg. 

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