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Many pools ask swimmers to shower before getting in the water, and a new study has highlighted the grim reality of why this is.

Tests on water collected from indoor swimming pools in the US discovered that everyday pharmaceuticals, such as makeup, could be reacting in a harmful way with the chlorine in the pool.

The analysis found traces of chemicals typically found in skin care products, insect repellent and flame retardants, all of which have the potential to be ingested by swimmers.

Tests on water collected from indoor swimming pools in the US discovered that everyday pharmaceuticals, such as makeup, could be reacting in a harmful way with the chlorine in the pool. The analysis found traces of chemicals found in skin care products and insect repellent that have potential to be ingested by swimmers

Chlorine is added to swimming pool water to keep it clear of certain bacteria.

Previous research has shown that elements of urine including urea, uric acid, and amino acids, interact with chlorine to produce potentially hazardous disinfection by-products in swimming pools.

And this new research suggests chemicals from pharmaceuticals and personal care products, or PPCPs, could be causing a similar effect.

'The whole motivation for examining pharmaceuticals and personal care products is that there is this unknown potential for them to bring about undesired or unexpected effects in an exposed population,' said Professor Ernest Blatchley from the Lyles School of Civil Engineering and the Division of Environmental and Ecological Engineering at Purdue University.

'There are literally thousands of chemicals from pharmaceuticals and personal care products that could be getting into swimming pool water.'

A research group led by Ching-Hua Huang, a professor in the School of Civil and Environmental Engineering at the Georgia Institute of Technology, recently developed a technique that identifies and quantifies 32 pharmaceuticals and personal care products in water.

'Because professor Huang had already developed an analytical method, we thought, "Why not use it and see what we find in swimming pools?" said Professor Blatchley. 

Water samples were taken from indoor swimming pools in Indiana and Georgia.

Of the 32 chemicals investigated, the researchers detected three in particular.

The first was N,N-diethyl-m-toluamide, known as Deet, and is an active ingredient in insect repellants.

Caffeine was also detected, as was tri(2-chloroethyl)-phosphate (TCEP). 

'The other 29 could have been present at concentrations below the detection level,' Professor Blatchley said.

'And because there are literally thousands of pharmaceuticals, this is just a small subset of compounds that could be present in swimming pools.

Pharmaceuticals may get into swimming pool water from personal care products applied to the skin such as insect repellant, makeup (stock image) and sunscreen. Many pharmaceuticals that are ingested are not fully metabolised by the body and are excreted in sweat and urine

'The main issue is that the release of chemicals into a place like a swimming pool is completely uncontrolled and unknown. I don't want to be an alarmist. We haven't discovered anything that would be cause for alarm right now, but the bottom line is we just don't know.'

Some chemicals are volatile, which means they can escape into the air to be inhaled. Others can be ingested or absorbed through the skin.

'Swimmers are exposed to chemicals through three different routes: You can inhale, you can ingest and it can go through your skin.

'So the exposure you receive in a swimming pool setting is potentially much more extensive than the exposure you would receive by just one route alone,' Professor Blatchley said. 

Pharmaceuticals may get into swimming pool water from personal care products applied to the skin such as insect repellant, makeup and sunscreen.

Many pharmaceuticals that are ingested are not fully metabolised by the body and are excreted in sweat and urine.

'Urine, I think, is really the primary mode of introduction,' Professor Blatchley said. 

'When it comes to pharmaceuticals, these are chemicals designed to be biologically active at pretty low concentrations. 

'Birth control pills, for example, contain hormones. If those chemicals and others are present, especially in a mixture in a water sample that humans are going to be exposed to, then what are the consequences of that? 

'That is a largely unanswered question.'  

The findings are published in the journal Environmental Science and Technology Letters.

However, Steve Levan, chairman of the Bromine Science and Environmental Forum (BSEF) told MailOnline: 'Brominated flame retardants consist of more than 70 different chemical substances with different properties.

'In fact, there is a wide range of reactive, polymeric, halogenated, phosphorus, mineral and many other types of chemicals that act as flame retardants, often applied in combination.

'This variety is necessary because the materials and products which need to be rendered fire-safe are also very different in their nature, their composition, and indeed their application. 

'The term "flame retardant" only describes the function of a substance and not its chemical nature which determines the properties of the substance. 

'Properties or findings from one substance should not be attributed to an entire family of chemical.'

He continued that BSEF has 'proactively taken responsibility' for the products it puts on the market, to reduce emissions of flame retardants at production phase by implementing best practices.