Biological monitoring and evaluation of potential hazards arising from the use of permethrin treated protective clothing for employees in the forestry sector

Status:

completed 12/2011

Aims:

Exposure to ticks poses a substantial biological hazard for forestry workers. Since for some tick-borne diseases such as lyme borreliosis there is currently no vaccination or chemoprophylaxis available, prevention of tick bites is crucial for health protection. Besides the application of tick repellent substances onto the skin especially the use of suitable clothing can be considered as an important protective measure in this context. Regarding experiences from the military sector there is some evidence that protective activity of clothing towards ticks can be enhanced significantly by finishing the fabric with the acaricide permethrin. Based on these findings and further laboratory testing, permethrin treated clothing for forestry workers has been developed and brought to the market some time ago.

Clothing used for military purposes has been extensively evaluated in the past regarding its benefits and possible risks arising from the permethrin impregnation. In contrast, comparable data is lacking up to now regarding clothing offered for forestry workers. Therefore, it is the objective of this project to examine the protective activity of commercially available clothing against tick bites on the one hand. On the other hand permethrin exposure as well as potentially associated health effects should be studied in wearers of permethrin treated clothing for forestry workers.

The results of our practice-oriented investigations are supposed to facilitate a profound risk-benefit analysis. Based on these findings recommendations for a safe use of this clothing as personal protective equipment should be given.

Activities/Methods:

This research project, which is based on a field study with 171 male employees in the German forestry industry, deals with the protective effects of permethrin impregnated forest protection trousers against ticks. Other aims were to investigate the internal exposure to permethrin and potential stress reactions of the human body. A complementary experimental study with 28 male test-subjects investigated - under strictly controlled conditions - factors which influence the absorption of permethrin and its possible routes of uptake.

Results:

• Persons wearing outdoor trousers without cut protection (predominant professional group: precinct commanders) are at particular risk of tick bites compared to those who wearing cut protection pants (predominant professional group: forest managers).
• Trousers impregnated with permethrin did not provide a significantly greater protective function against ticks than none-impregnated trousers among the sample of employees wearing cut protection pants. In contrast, for the sample of employees wearing impregnated trousers without cut protection a significant reduction of tick infestation was found. Nevertheless, using permethrin treated pants could not totally prevent tick infestation on the legs, still requiring scanning for ticks after work.
• Under our study conditions no relevant stress reactions were observed when wearing permethrin impregnated trousers. However, there remains a potential but unlikely risk of a permethrin allergy.
• Wearing permethrin treated trousers is connected to a (mainly dermal) uptake of permethrin, which is to some extent considerably higher than in the general population. There is no exceedance of the acceptable daily intake (ADI), defined by the WHO. However, a weak carcinogenic potential of permethrin in humans cannot be finally evaluated due to data gaps at present.
• Internal exposure and permethrin uptake respectively was influenced, amongst others, by the particular type of pants used, the manufacturer, period of use, climatic conditions and physical work load.
• Considering the results on protective efficacy and toxicological aspects, a general and undifferentiated use of permethrin treated trousers for forestry work cannot be recommended. Instead, it seems to be reasonable to select potential users carefully and individually and to use respective clothing under the premise of exposure minimization.

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