Oh dear. The newspapers this morning are reporting that
Here's the study. Young fish were exposed to a combination of three drugs, two antidepressants and an epilepsy med, for 18 days.
First off, this study was tiny with an effective sample size of just 6. Three tanks of fish got exposed to the drugs, and three control tanks didn't. There were multiple fish per tank, five in fact, but those are not five independent observations, because they shared a tank. That's just tiny for a drug trial, or any scientific study really.
Next, the drug doses were much higher than in the water supply. Levels of fluoxetine (Prozac) were 700 times higher than observed in drinking water, for carbamazapine it was 400 times higher. And that's based on the authors' figures for drinking water which they admit are "the highest observed concentrations from various systems". The authors defend this by saying that in drinking water there will be other related compounds, on top of the drugs themselves, adding up to a higher dose. OK - but 400, 700 times higher? We've no idea if that's realistic. They don't justify this number.
What did the drugs actually do to the fish? After 18 days of exposure to the drugs, the fish - juvenile fathead minnows - had their brains removed and the expression levels of various genes measured using a genetic microarray.
The drugged minnows had significantly increased expression of a set of 324 genes dubbed "autism genes" ("autism_ideopathic" in the paper.) I'm not going to get into the question of whether these really are autism genes in humans, or whether fish brains are a good of model of humans. Those are hard issues. But what's easy to see is that while this set of genes were apparantly increased, so were many others.It was not specific to 'autism genes'.
The autism genes were upregulated by an average factor of +1.621... but this was only slightly more than the "Parkinson's Disease genes" at +1.56 and the "Multiple Sclerosis" ones at +1.375. Meanwhile, "Bipolar Disorder" genes were down by -1.172. So if antidepressants in the water are causing autism, they're probably also causing (or preventing!) a lot of other problems too.
The authors note that only three of the gene sets were statistically significantly altered, but that doesn't mean those sets were special, this is the fallacy of treating differences in significance levels as evidence of significant differences.
Of 10 more specific "autism gene" sets that they also examined (in the same fish), all were increased by various amounts (+1.050 to +1.537), some of which were significant - but one of those was a set of genes previously reported decreased in autistics, not increased (it was the "synapse" genes from this study).
What these changes in gene expression mean is anyone's guess. Given the small sample size they could be just noise. If not, all they really show is that levels of psychoactive medications that are quite low, but much higher than in drinking water, have affect the brains of fish. We don't know what that effect means, for the fish, let alone humans.
Early life antidepressant exposure might cause autism. I don't know. Stranger things have happened. We know that fetal anticonvulsant exposure can do it but that's when mothers are actually taking the pills. It's one giant leap from that to traces in drinking water. It's the difference between falling off your chair and falling off the Empire State Building.
Michael A. Thomas, and Rebecca D. Klaper (2012). Psychoactive Pharmaceuticals Induce Fish Gene Expression Profiles Associated with Human Idiopathic Autism PLoS ONE