Household spray warning- problems with pyrethroids

Mounting concern in Germany over the health effects of synthetic pyrethroids used as household insecticide sprays may lead to a ban on their use. A study earlier this year indicated a link between cancer and these sprays (see PN 28) and a new study suggests that pyrethroid poisoning may be affecting people using pyrethroid sprays. Symptoms have included damage to the central nervous system, dizziness, headaches, diarrhoea and panic attacks. The German Ministry of Health has drafted a proposal to ban these products, which is awaiting a departmental vote. Heike Schmitt investigates these issues.

Synthetic pyrethroids have been on the market for several decades. They are derived from pyrethrins, extracted from a variety of the Chrysanthemum flower native to Kenya. Synthetic pyrethroids were designed with greater persistence to enhance shelf-life. The perceived advantage was their relatively low mammalian toxicity, but a broad spectrum of activity against insects has meant they can kill not only pests but also the natural predators of pests. New German research raises further concern, linking synthetic pyrethroids to chronic health effects. The German Federal Institute of Public Health has advised consumers to keep use as low as possible.
    If confirmed, the results of this study will have considerable significance, as synthetic pyrethroids are widely used in the home and in closed environments such as glasshouses and horticulture. A recent US survey draws further attention to the problems of home use of pesticides, and particularly the effect on children(1). “Indoor air use of pesticide products in the home is the main source of exposure for children,” says toxicologist William Pease of the University of California-Berkeley School of Public Health, who also believes exposures from household use exceed those from pesticide residues in food.

New study—chronic concern
At a seminar of experts in Berlin in March 1995, Professor H. Müller-Mohnssen summarised the symptoms of one hundred patients suffering from pyrethroid poisoning. Some had acute symtoms and some had chronic symyoms lasting over a period of years(2).
    The cases were selected from 500 patients according to a number of criteria. Chronic exposure was measured by residues in either in urine or dust. The effects of other types of pesticide active ingredient were eliminated by selecting cases where exposure could be restricted to formulations containing pyrethroids only. Cases were used only where there was an appropriate interval between exposure and the onset of symptoms, or between cessation of exposure and the reduction of symptoms. Only cases involving adults were considered. The patients comprised pest controllers and private users, including owners of treated textiles, especially carpets, users of electric vaporisers (small boxes containing pyrethroid formulations) and users of wood preservatives.
    A total of 24% suffered acute poisoning symptoms following application of pyrethroids. Although air concentration decreases rapidly after spraying, initial concentrations can be as high as 500µg/m3 (parts per billion)(3). Sub-acute poisoning, with a latency period of 2-6 days, occurs when electric vaporisers, are used within distances of less than 50 cm from the face. Poisoning can also occur when working in a room that was sprayed two days previously. Just over half of the cases (57%) showed symptoms of poisoning after repeated or even single exposure following spraying or use of a vaporiser. Although air concentrations may be as small as 0.01 µg/m3, concentrations may be greater in dust and on textiles—generally more than 10 mg/kg in dust.

Poisoning symptoms
Typically synthetic pyrethroids affect the nervous system and acute exposure can lead to parasthaesia and irritation of the eyes, mouth, and the respiratory system. Disorders of the central and autonomic nervous system can follow: nausea, dizziness, headaches, diarrhoea, sweating and panic attacks. The condition can worsen for 2-6 weeks afterwards, giving rheumatic pains, squinting, asthma-like symptoms and difficulties in walking, writing and speaking. In a plateau phase (lasting 2-6 weeks), lethargy, aggression and depression may occur. Chronic effects can include multiple chemical sensitivity (MCS) and neurological damage: some 40% of cases resulted in MCS.
    Inert ingredients, as a possible cause of ill-effects in sprays, have been discounted  because symptoms were similar for sprays and electric vaporisers (which do not contain inerts).
    Interpretation of the results would be assisted by further details of case selection and statistical analysis. We understand that the latter aspect cannot yet be published because of issues of confidentiality. Nevertheless, the results are of sufficient significance that further research should be treated as a matter of urgency. The German agrochemical industry association disagrees, saying that the proposed ban on synthetic pyrethroids is politically motivated and is not based on scientific evidence(4).  The ban suggested by the German Ministry of Health would not extend to ‘short-life’ pyrethroids, nor professional use of pyrethroid products.

Pesticides Trust [now PAN UK] comment
As the study by Professor Müller-Mohnssen is yet to be corroborated, it would be prudent to wait before making a final judgement. Clearly a public airing on this research would facilitate open discussion.
    In the meantime, less toxic alternatives can be used in the home and public demand for alternatives is increasing. In many cases effective alternatives are yet to be developed. For other pests they exist, for example, silicon dioxide provides an effective and safer control against household and pet animal pests (see p16). There is need for a comprehensive research programme into the chronic effects of widely-used household pesticides and development of non-toxic replacements.

1. Grossman, J., Dangers of Household Pesticides, Env. Health Perspectives, 103:6, 550-54, 1995.
2. Müller-Mohnssen, H., Über eine Methode zur Früherkennung neurotoxischer Erankungen (am Beispiel der Pyrethroidintoxikation), Gesundh.-Wes. 57, 214-222, 1995.
3. Walter, G., Keller, R., Beckert, J., and Budde, W., Anreichung von Bioziden in Innenräumen am Beispiel der Pyrethroide. Zbl. Hygiene 195, 450-456, 1994.
4. Agrow 30 June 1995.

Heike Schmitt is from Germany and is currently seconded to the Pesticides Trust [now PAN UK].