March 1, 2017

pyrethroid insecticides in pregnancy and in children, and childhood behavioural difficulties

Researchers publishing in the Occupational & Environmental Medicine investigated the associations between prenatal and childhood exposure to pyrethroid insecticides and behavioural skills in 6-year-olds. Roundup comments accompanied this analysis.

Title, Date of Publication & Journal

‘Behavioural disorders in 6-year-old children and pyrethroid insecticide exposure: the PELAGIE mother-child cohort’ by Jean-François Viel et al.

Published in Occupational & Environmental Medicine on Wednesday 1 March 2017.

Study’s main claims – and are they supported by the data

The evidence presented in the paper provides only weak support for the suggestion that exposure to certain pyrethroids at the low environmental doses encountered by the general public may be associated with behavioural disorders in children, because there are significant study limitations, the authors used 30 tests of statistical significance and only two were significant, and the most extreme finding was actually an association between one urinary metabolite and a reduced rather than increased risk of a certain behavioural disorder.

An important sentence in the press release is: “This is an observational study so no firm conclusions can be drawn about cause and effect, added to which accurately assessing pyrethroid exposures using urine samples is notoriously difficult because metabolites are cleared from the body in just a few days.”

Strengths/Limitations

Strengths

Even though the authors performed multiple tests, the in vitro evidence for what they found is quite good.

Everything is sensible in terms of internal consistency, e.g. dose responses and randomisation/blinding of the investigators.

In vivo data seems to support anti-oestrogenic activity, but these are large doses and may be unrealistic in humans or in the real world.

Limitations

BHPF was detectable in 7 out of 100 students’ serum who drink water regularly from bottles. This was not compared to students who did not drink regularly from water bottles and therefore we cannot tell if it was other factors that could have affected these levels found. (For example, if those who drunk regularly from a bottle of water were more likely to go to the gym then it could be that the gym shower water increased the amount of BHPF in the serum).

As the press release correctly states the bottles of water were not measured to gauge their levels of BHPF. So we do not know how much BHPF the bottled water contained, if any at all.

How the BHPF got into their serum is not known and therefore this finding could be as a result of anything/from anywhere – i.e. maybe it didn’t come from the bottles at all.

The concentrations used in mice weren’t justified or explained what the equivalent levels would be in humans i.e. is 50mg/kg the dose expected to be the safe/normal levels in humans?

The bottles were filled with hot water and then left to cool, because people in China usually use water in this way. This is not the case in the UK. So does the heating affect the BHPF levels released into the water?  In other words, are these findings applicable to the UK even if they are real?

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