Case Studies - Release of Chloramines from Swimming Pools & Processing of Salad Vegetables

What is the connection between swimming pools and lettuce processing? Answer: a group of chemicals known as chloramines.

It is generally known that chlorine is used to disinfect the water in swimming pools. On its own this is not usually a problem but when bathers enter the water they introduce organic matter, such as urine, which can react with chlorine to form chloramines. The three chloramines (mono- and dichloramine and nitrogen trichloride) are known to cause eye and respiratory irritation. Nitrogen trichloride is of particular concern. It is hydrophobic and readily outgases from the swimming pool water into the atmosphere, potentially exposing attendants who might spend much of their working day at the poolside.

It may be less well known that lettuce and other salad vegetables are washed in water containing chlorine before being packed for the ready-to-eat market. When the vegetables are cut during preparation, they release sap proteins which, in the presence of chlorine, form chloramines to which the packers may be exposed.

In the UK there is no occupational exposure limit for chloramines and very little is known about the extent of workplace exposure. To fill this knowledge gap, a survey was carried out to measure exposure of swimming pool attendants and personnel engaged in lettuce preparation. The properties of the three chloramines are quite different so a two-stage sampling device was required: mono- and dichloramine were trapped on the front section of the sampler and analysed electrochemically; nitrogen trichloride was collected on the rear section and measured by ion chromatography.

French researchers have proposed an upper limit value and a 'comfort' limit value for exposure to nitrogen trichloride based on its irritancy effects. A few of the results from the swimming pools indicated exposures that were at or just above the proposed 'comfort' limit, but most results were significantly lower. All the exposures recorded during lettuce processing were well within the proposed limits. These data have contributed to an assessment of the risks associated with exposure to chloramines in two quite diverse occupational groups.

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