UVc Irradiation & Sunlight  in swimming pools or chlorinated system

The following report represents the opinion of Dryden Aqua based on the available data in the literature and the experience of Dryden Aqua. A research program is also in progress to determine the impact of UVc irradiation of chlorinated water. The information conflicts with the reports from research sponsored by, or reported by the industry. Dryden Aqua do not have a vested interest in UVc irradiation systems, our concern is only with public health and the well-being of pool staff,  and the desire to make swimming a healthy and safe activity.

The problems relate to all chlorinated swimming pools exposed to UVc irradiation from sun-light,  either out-door pools or indoor pools with large windows and from UV irradiation systems, especially medium pressure units.  There are many reactions that take place with dissolved components and chlorine in the water and UV light  can provide the energy required to produce more volatile and exotic chemicals.  Chlorine by-products such a inorganic chloramines will be reduced, indeed THM levels will also be reduced in solution.  However because the  by-products have a tendency to be smaller and more volatile when manufactured by UV, the concentrations will drop in the water as the chemicals escape to enter the air, but they will increase in the 50mm air space just above the surface.  For bathers the air space just above the surface of the water is very important, and applies to all pools, even with good ventilation or out-door pools. The air quality above the water surface is not monitored, yet concentrations of toxic gas may exceed short term HSE exposure limits. 

An adult human lung has some 70 square meters of surface area and is designed for gas diffusion, and if you have lipid soluble gases such as chloroform, or cyanogen chloride there is little to stop then from passing into your blood, or even across you blood brain barrier to your nervous system.   We know that this is happening, what we don't know is the potential long term damage the by-products  may cause on the health of children and adults, 10, 20 or even 40 years after an exposure. Cyanogen chloride is one of the main reaction products, the UK HSE give a short term exposure  limit of 0.3ppm for 15 minutes. However cyanogen chloride was developed as a nerve gas and we really do not know the impact very low levels have on children under 2 years old that do not have a fully developed blood : brain barrier. Dryden Aqua are marine biologists specialising in the aquaculture industry, there are many factors that can cause fish stress and disease and thereby affect the profitability of the farm.  Many of the problems in fish farms are known but not quantified,  however it is a standard procedure to eliminate problems and potential problems, as opposed to adopting a wait and see approach and count the number of fish that have died. It is the opinion of Dryden Aqua that the same policy should be adopted with the swimming pool industry.

Medium pressure UVc irradiation of water will reduce inorganic as well as organo-chloramines and dissolved organics. UVc irradiation of  chloramines and dissolve organic matter in the presence of chlorine may also form chlorine reaction products such as the THM chloroform and extremely toxic gas such as cyanogen chloride. The volatile chlorine reactions products rapidly exit  through the water surface and concentrate in the air space just above the water. Even if the pool has a good ventilation system, or if it is an out-door pool, there may still be a higher partial pressure of chlorine reaction products on the water surface. Chlorine reaction products in air are much more toxic than the chemicals in solution because lung tissue is designed for gas diffusion. The toxic implications of THM's and cyanogen chloride are reported in the literature. 

Most of the data presented for swimming pools has centred on the dissolved chemical concentrations, a full mass balance of chlorine has  rarely been conducted and only a few trials have included the air just above the surface of the water.  UV irradiation will reduce combined chlorine and will allow you to operate with lower chlorine levels, but you need to ask the questions what else is happening ? and are even more toxic chemicals being produced that you can not smell  or easily measure. Dryden Aqua consider the reporting of information regarding UVc irradiation has been selective and does not portray the complete picture.

In order to answer some of these questions, Dryden Aqua have now started to monitor air quality just above the water surface for chlorinated reaction products in pools with and without UVc irradiation. To-date we have found that pools using medium pressure UV will on average use a great deal more energy, chemicals and water that pools that do not use UVc.

If you operate a swimming pool with a UV and would like to take part in our survey, then we ask you to complete the following table, after week 4 turn the UV off but continue to monitor the quality of the water, after week 8 turn the unit back on again.  If the pool has a deficient water treatment system, then the trichloramine levels will increase, and there may be an increased risk of bacteria and cryptosporidiosis. The responsibility to run the test is with the pool operator, Dryden Aqua accept  no liability for any consequences in turning off the UV unit.  Dryden Aqua is developing on-line simple low cost analysers for chlorine reaction products, we can then progress and conduct the tests for a second time with a full mass balance of the chlorine and chlorine reaction products.  The data will be audited by an independent laboratory and reviewed by an organisation with no vested interest in the pool industry or UV manufacturing.

Chloramine such as nitrogen trichloride is dangerous and UVc irradiation of the water reduces nitrogen trichloride concentrations in the water and air,  but we do not know what else is happening to the air quality just above the surface of the water. We may be forming a host of extremely toxic lipid soluble  gases that can cause organ and nervous system damage, especially to children. Questions need to be asked and data collected, so your help in completing the survey would be appreciated.

Additional reading

1. Danish Technological Institute Department for Swimming Pool Technology  download (1)  &  download (2)

2. Swimming pools and the risk of spinal deformaties years latter with children; download 1,  download 2,  download 3