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Monochlorophenols

Report

To read the report please click here.

Summary

Current levels of monochlorophenols in the surface waters and sediments are unlikely to pose a risk to the marine environment in the North Sea region. This conclusion is based on 79 aquatic toxicity tests, plus monitoring data from estuarine/marine and river waters and sediments. Monochlorophenols are neither persistent nor bioaccumulative.

Applications and emissions of monochlorophenols

Monochlorophenols are used as chemical intermediates. There are three types: 2-chlorophenol, 3-chlorophenol and 4-chlorophenol. Between 2,000 and 3,000 tonnes per year of 2-chlorophenol and 4-chlorophenol each are produced in the Mediterranean region. Nearly 100% of 2-chlorophenol and 70% of 4-chlorophenol production is used in further synthesis in the North Sea area. Less than 1,000 tonnes/year of 3-chlorophenol is produced in Europe.
Nature also produces 4-chlorophenol.

Euro Chlor has monitored industrial emissions of 2- and 4-chlorophenols. Between 1985 and 1997 emissions of 2-chlorophenol to air fell from 3,200 kg/y to zero and emissions to water decreased from 150 to 70 kg/y. In the same period, emissions of 4-chlorophenol, which are only to wastewater, were reduced from 2,000 to 70 kg/y.

Evaluation of environmental risk

Risks associated with the use of any substance are determined by the hazard properties of the substance and exposure to it.

Two scenarios were considered in the marine risk assessment of monochlorophenols. They were the assessment of toxicity to aquatic organisms and to organisms living in sediments.

Hazard assessment

Aquatic organisms

For 2-chlorophenol, the evaluation of aquatic toxicity was based on 33 test results, including 7 for fish, 4 for invertebrates and 2 algae, which were identified as being valid for risk assessment purposes. A further 9 for fish, 4 for invertebrates and 2 for algae were judged valid, but considered with care.

For 3-chlorophenol, the evaluation of aquatic toxicity was based on 9 test results, including 1 for fish, and none for invertebrates or algae, which were identified as being valid for risk assessment purposes. A further 2 each for fish, invertebrates and for algae were judged valid, but considered with care.

For 4-chlorophenol, the evaluation of aquatic toxicity was based on 37 test results, including 4 for fish, 6 for invertebrates and 2 for algae, which were identified as being valid for risk assessment purposes. A further 4 for fish, 8 for invertebrates and 5 for algae were judged valid, but considered with care.

The toxicity data for the different monochlorophenols were comparable, so it was concluded that the three substances have similar toxicity. There appears to be a similar sensitivity between freshwater and marine organisms to monochlorophenols, although there was limited data for marine organisms.
Pooling all the chronic data of the three types of monochlorophenol, and applying an assessment factor of 10 to the overall lowest No Observed Effects Concentration, results in a worst-case PNEC (Predicted No Effects Concentration) of 30 µg/l.

A PNEC for sediments, which according to the EU TGD (Technical Guidance Document on risk assessment) can be based on the PNEC for water while assuming equilibrium partitioning is calculated at 258 µg/kg ww.

Exposure assessment

The concentrations of monochlorophenols in river and sea are provided (see figure: North Sea monitoring data on monochlorophenols). Monitoring data from 1974-86 indicate concentrations of 2-chlorophenol of 0.05 to 2.3 µg/l in various surface waters. More recent data from The Netherlands and UK show that in most locations the concentrations of 2-, 3- and 4-chlorophenol is under the detection limit of 0.1 µg/l in surface water and 0.1 mg/kg for sediments. For 2-chlorophenol, 90% of the reported values were under 0.5 µg/l, and this figure was used as the worst-case Predicted Environmental Concentration for water in final risk calculations. Typical PEC in water was set at 0.1 µg/l. For sediments, a Predicted Environmental Concentration of monochlorophenols of 125 µg/kg was based on 1996-1997 data from The Netherlands.

Based on their low octanol-water partition coefficients, monochlorophenols are expected to have no potential for bioaccumulation, which was confirmed by laboratory tests. Monochlorophenols photodegrade in water. Secondary sewage treatment plants biodegrade a high percentage of 2- and 4-chlorophenol at concentrations of less than 10 mg/l. Biodegradation of monochlorophenols in river sediments, soils and in anaerobic conditions is also high. Based on testing to-date, monochlorophenols should be classified as inherently biodegradable.

Risk assessment conclusions

The risk assessment was based largely on the methodologies prescribed by the EU-TGD where the ratio of the predicted environmental concentration (PEC) to the predicted no effect concentration (PNEC) is used as an indication of risk. A ratio of less than 1 indicates no risk—the smaller the number, the greater the assurance of low risk related to the assessment.

The natural production of monochlorophenols was not included in the risk assessment. As the three monochlorophenols exhibit similar toxicity characteristics, they are treated as one substance.

Aquatic organisms

The PEC/PNEC ratio for monochlorophenols in surface water was 0.02 for the worst-case scenario, and typically less than 0.003, indicating that levels of monochlorophenols in the surface waters of the North Sea were unlikely to represent a risk to the marine environment.

Organisms living in sediments

The PEC/PNEC ratio for monochlorophenols in sediments was 0.48 for the worst-case scenario, and typically less than 0.19, indicating that monochlorophenols do not pose a risk to sediment-dwelling organisms in the North Sea.

North Sea Monitoring Data on Monochlorophenols