SPRI Home About SPRI

Halogenated organic compounds - total as AOX

SPRI Emission Reporting Threshold
1,000 Kg/yr Pollutant Emissions to Land
1,000 Kg/yr Pollutant Emissions to Water
1,000 Kg/yr Pollutant Emissions to Waste Water
This sheet is a generic summary, designed to give the reader a basic level of background information about the substance in question. Great care has been taken to represent as effectively and correctly as possible the broad range of (not necessarily consistent) information which is available from a variety of sources. The reader must accept therefore that this sheet has no legal status and cannot be relied upon in any legal proceedings. SEPA disclaims any responsibility or liability whatsoever for errors and omissions in this sheet.
What is it?
Adsorbable organically bound halogens (AOX) are a group of chemicals which can be adsorbed from water onto activated carbon. Most AOXs are compounds containing chlorine, but some also contain the similar elements bromine or iodine. The properties of AOXs vary: some evaporate easily (such as trichloromethane or chloroform); some are complex molecules such as dioxins and furans.
What is it used for?
Most AOXs do not have a specific use and are not intentionally manufactured.
Where does it come from?
The main sources of AOX are from the chlorine chemicals used to bleach fibres in the paper and pulp industry. Smaller amounts are also formed during the routine chlorination (disinfection) of drinking water, swimming pools and industrial effluents.
How might it affect the environment?
Some AOXs are toxic to fish and aquatic organisms - even at low concentrations. Many are persistent and have a tendency to accumulate in the environment which causes concern at a regional (if not global) level.
How might exposure to it affect human health?
Exposure of AOXs to humans can occur through eating contaminated food - and the fact that AOXs can concentrate up the food chain means that humans could be exposed to dangerous levels. The type and severity of adverse effects depend on the AOX in question. Some (such as dioxins) are known to be very toxic. It is however unlikely that concentrations would reach dangerous levels in food in the UK.
What steps are being taken to limit the potential impacts?
In the UK (including Scotland) releases of AOX are controlled through the Pollution Prevention and Control (PPC) regulations. Chlorinated AOXs have been on the European Commission's "black list" of toxic substances since 1976.