It has already been shown how many of the water systems in Europe are polluted with synthetic hormones derived from contraceptive pills, to such an extent that they have even been linked to the collapse in some fish populations, resulting in the suggestion that we need a massive clean-up operation. The impacts seen in fish are not currently thought to harm people, but the notion that everything we consume could have traces of pharmaceutical drugs is a persistent one.

It is this claim that spurred a new study to examine how the reuse of wastewater to irrigate crops might also be cycling pharmaceutical drugs. The research claims to have found that traces of the drug carbamazepine, usually used to treat epilepsy, can be found in the urine of people who have consumed vegetables grown using recycled water taken from households. They suggest that the drug, which enters the water system when a person taking it pees and flushes the toilet, is circulating between produce and people, via pee.

The drug is commonly found in wastewater, which is why the study focused on seeing if the consumption of vegetables grown using such water increased the concentration found in the participants' urine. As water security becomes more of an issue and water shortages more frequent the use of waste water to irrigate crops is also increasing in occurrence, especially in places such as Israel where an estimated 50 percent of crops are now watered in such a way. It was for this reason that the latest paper focuses on those from Israel.

The study, published in the journal Environmental Science & Technology, wasn’t particularly rigorous, though. Using a sample size of just 34 people, they divided the group into two. The first group was given produce irrigated with wastewater for a week, and then vegetables watered with clean water, while the second group was meant to receive the reverse. But the researchers claim that they ran out of the original batch of produce irrigated with wastewater, and admit that they had to use locally sourced vegetables, which they suspect were a mixture of both wastewater and clean water fed.

At the beginning of the study, they report that the participants all had mixed levels of carbamazepine, but that after one week of eating wastewater irrigated produce, the first group all reported having quantifiable levels of the drug in their urine. After switching to the other, clean water fed vegetables, the researchers note that the levels of the drug dropped again. With the second group, little could be drawn from it, as the levels of the drug in their urine remained relatively constant.

The study claims that the fact the levels of carbamazepine detected in the first group were up to a quarter of what you would expect to find in people actually taking the drug is proof of concept that this pee-food-pee cycle does exist. But people have not doubted that there are pharmaceuticals in our drinking water and food. What is under question is whether or not these levels are high enough to have an effect, and so far the results remain inconclusive.