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Mercury

Report

To read the report please click here.

Background

Scope of the Euro Chlor Risk Assessment Programme - Euro Chlor voluntarily agreed in 1995 to carry out risk assessments of 23 chlorine-based compounds, focusing on the marine environment. Data was collected and evaluated on the effects and environmental concentrations of these compounds. The products are on the lists of concern of European countries participating in the North Sea Conference.

Goals - The risk assessments aimed to explore whether the 23 chlorine chemicals posed a risk to the marine environment, especially the North Sea.

Data sources - The effect data was derived from laboratory toxicity tests. Exposure data came from analytical monitoring programmes. Where necessary, the exposure data was backed up with calculated concentrations based on emission models. All data came from validated, published sources. Toxicity data was sourced worldwide; monitoring data was from Europe only. A primary source of data is the HEDSET file on each compound.

Other programmes underway - A formal programme under the EU Existing Substances Regulation (793/93) is also assessing human health and environmental risks of a range of compounds, including some chlorine-based chemicals. This is designed to widen knowledge about marketed products. Euro Chlor members are co-operating on these with member state rapporteurs.

Risk assessment methodology - For the voluntary risk assessments of 23 chlorine-based compounds - aimed at evaluating the risks linked to given products - Euro Chlor followed the EU guidelines (1488/94) published under the Existing Substances Regulation (793/93). The three steps used in all Euro Chlor risk assessments were:

1. Predicted no-effect concentration (PNEC) - An evaluation of the hazard based on (eco)toxicological characteristics. The use of this data to derive the PNEC, the level of chemical at which no effects on the environment would be expected. Three different levels in the marine food chain were examined: aquatic plants (primary producers), invertebrates (primary consumers) and fishes (secondary consumers).
2. Predicted environmental concentration (PEC) - An estimation of exposure of the marine aquatic environment based on real data from monitoring programmes. This allowed a PEC to be derived.
3. PEC/PNEC - A comparison between PNEC and the actual exposure level, expressed by the predicted environmental concentration (PEC). If PEC is lower than PNEC, the product poses no risk; if it is equal to or higher than PNEC, management measures have to be taken to reduce the exposure to an acceptable level.

Overall, a risk assessment can indicate that there is (i) a need for further information or testing; (ii) at present no need for further information or testing, or no need for risk reduction measures; or (iii) a need to limit the risks.

Summary

Current levels of mercury as a general pollutant from different sources in the OSPAR area do not represent a significant risk to the marine environment. This conclusion is based on 124 laboratory ecotoxicity studies for inorganic mercury and 27 laboratory ecotoxicity studies for organic mercury, plus monitoring results from the North Sea coastal waters, estuaries and sediments. Evaluation for organic mercury secondary poisoning potential demonstrated no high-risk concern. Trends over 1974-1995 show a six-fold decrease of mercury levels in river waters whilst levels in marine biota generally remained constant over the same period. Coupled with a more than 10-fold decrease in emissions from the European chlor-alkali industry in the same period, it is unlikely that any future reductions from this source would significantly change the North Sea situation.

Sources of mercury

Natural sources of atmospheric mercury include:

• Erosion and degassing of mineralised soils - estimated to account for 700 tonnes/year based on flux measurements, with 500 tonnes/year coming from mercury-rich belts of soil.
• Volcanic eruptions and geothermal activities - volcanoes release some 830 tonnes/year of mercury, 95% from active erupting volcanoes.
• The earth’s subsurface crust - mercury escapes through faults and fractures in bedrock, conservatively estimated to account for 1,000 tonnes/year, excluding mercury entering deep oceans directly.

Anthropogenic or man-made mercury emissions account for some 870 tonnes/year in the Western world, or about 15% of total global anthropogenic emissions (5,600 tonnes/year.) Around 30% of these are re-deposited locally or regionally, leaving about 4,000 tonnes/year globally distributed in the atmosphere.

World mercury production is falling. In 1989, total production was over 5,700 tonnes. As a result of a reduction in European production to 400 tonnes in 1997, world production is believed to have totalled less than 2,000 tonnes in that year.

Mercury is used in various industrial processes and products, including dentistry, measuring and control equipment (such as thermometers and blood pressure measuring devices), batteries, lamps, and the chlor-alkali industry (where it is used as the cathode in electrolysis of sodium chloride solution to produce chlorine gas and caustic soda in closed cells.)

Emissions from the chlor-alkali industry are estimated to represent less than 10% of total anthropogenic emissions in Western Europe. For the OSPARCOM area total emissions were 8.5 tonnes in 1997 with only 0.5 tonnes losses to water. The chlor-alkali industry is committed to continued reductions in mercury emissions.

Evaluation of environmental risk

Toxicity

For inorganic mercury, 21 data for fish and amphibians, 68 data for invertebrates and 35 data for algae were evaluated according to the environmental quality criteria recommended by EU authorities. Both acute and chronic toxicity studies were taken into account and the appropriate assessment factors were used to define a final aquatic PNEC for inorganic mercury of 470 ng/l. For organic mercury, 11 data for fish, 9 data for invertebrates and 7 data for algae were used to calculate an aquatic PNEC of 10 ng/l.

Based on limited data confirmed by extrapolation from water effect levels, a PNEC in sediment of 31.2 mg/kg and 1.2 mg/kg wet weight was calculated for inorganic and organic mercury, respectively.

Potential for secondary poisoning was evaluated in large and small fish-eating predators, assuming presence of all mercury in tissues in the organic form. A lowest reference dose (or tolerable daily intake) for aquatic predators of 18 µg organic mercury/kg body weight/day was derived from duck and mink studies. Daily intakes of the predators, calculated from fish monitoring data, varied from 6 to 22 µg organic mercury/kg body weight. Safety margins were estimated at between 3 and 1 when comparing these intakes with the reference dose.

Monitoring data and risk characterisation

Monitoring data from river water were collected in 1994-97 in various European countries (B, D, F, I, NL, S and UK), including the Scheldt estuary, the North Sea, the Wadden Sea and the Rhine estuary. Temporal trends were analysed in UK river water from 1974-95. For sediment, data from three countries (D, F and NL) were used.

For inorganic mercury, highest total concentrations in coastal waters and estuaries found in recent years are up to 170 ng/l, giving a safety margin of up to 3 between PEC and PNEC.

For organic mercury, a worst case PEC of 8.5 ng/l was calculated, giving practically no safety margin. Trends in river mercury levels from the OSPARCOM area have shown a six-fold decrease.

For sediment, worst case PEC values of 1.6 mg/kg and 0.16 mg/kg wet weight for inorganic and organic mercury, respectively, give safety margins of 20 and 7.

Available data show that mercury is a persistent, toxic and bioaccumulative chemical. Its potential for secondary poisoning (food-chain biomagnification) and long-range transport make it a high priority for emission control. However, due to its natural occurrence, mercury will remain ubiquitous in the environment.

Risk assessment conclusion

Current monitoring data on mercury in coastal waters, estuaries and sediments do not demonstrate a significant risk to the environment, although the margins of safety between PECs and PNECs are sometimes close to 1, especially for animal species higher in the food chain and exposed to organic mercury. Levels in rivers entering the North Sea have been decreasing by a factor of six over the past 20 years whilst Euro Chlor emissions have decreased by a factor of 12 in the same time. However, mercury levels in marine biota (fish) have generally been constant over the same period. Based on these levels, secondary poisoning of marine birds or mammals is not of high concern. Although the European chlor-alkali industry is committed to continue mercury emissions reduction, it is clear from this study that these reductions will have little, if any, effect on the North Sea environment.

OSPARCOM Region - North Sea