CONCENTRATIONS OF GASEOUS TRACE ELEMENTS SUCH AS MERCURY IN THE AMBIENT AIR OF THE NETHERLANDS

ABSTRACT
Around the world, there is increasing concern about mercury in the environment. Sources of mercury emissions to the air include municipal waste incineration plants, coal-fired power plants and municipal sewage sludge disposal. The emission of mercury from coal-fired power plants in the Netherlands is well documented. However, to assess the environmental consequences of the emissions of mercury and other trace elements, it is necessary to know the background concentrations in the ambient air.

Over a period of a year, a measuring station was in operation at Arnhem (the Netherlands) to sample the ambient air. Active carbon was used as an adsorption medium: a method developed by KEMA. The sampling periods were one to two months, so that a total of nine duplicated measurements were made.

The ambient concentrations of the gaseous trace elements arsenic, boron, bromine, antimony, selenium, mercury and iodine in the air were determined. The averaged concentrations were as follows: arsenic 1.2 ± 0.15, boron 60 ± 2, bromine 50 ± 0.7, antimony 0.4 ± 0.06, selenium 0.8 ± 0.6, mercury 1.4 ± 0.15 and iodine 6 ± 1.7 ng·m^-3

On the basis of these results, it does not appear that the ambient mercury concentrations in this area are problematic.

1 INTRODUCTION
In order to study the environmental impact of coal-fired units in the Netherlands, it is necessary not only to quantify emissions and calculate immissions, but also to know the background ambient atmospheric concentrations. Only once these concentrations are known is it possible to determine the extent to which the situation is affected by the use of coal for power generation. The Dutch background concentrations of many elements and compounds were determined in 1982 and 1983 as part of the NOK-LUK programme (a  national research programme concerned with coal-fired plant and the associated pollution; PEO, 1985). However, the data on the environmentally significant element gaseous mercury was based upon measurements carried out over a mere two-month period at four locations. The average concentration suggested by the NOK-LUK research was 0.3 ng·m^-3, while data published elsewhere indicated that 4 ng·m^-3 was more realistic.

Meanwhile, concern about the presence of mercury in the environment has grown. Mercury has been recognised as an environmental hazard since the fifties, when many people in Japan died and still more contracted serious conditions of the central nervous system as a result of eating fish contaminated with mercury. Since 1984, a national research programme has been running in Sweden, looking at the impact of mercury on the environment. Like Canada and northern parts of the US, Sweden has a problem with mercury, because the granite bedrock reduces the soil’s buffer capacity. As a result, acidification easily occurs in lakes affected by acidic deposition. A side-effect of this process is that the mercury present in the humus layer is released by the acidic rainwater. The mercury in the humus layer is of anthropogenic origin, having accumulated as a result of deposition from the air over many years. The mercury concentrations in the water are not a direct threat to plants, animals or people. However, it appears that inorganic mercury is converted into methyl mercury, which can find its way into fish. Human consumption of fish affected in this way could cause poisoning similar to that which occurred in Japan. The Swedish authorities have accordingly set a limit on the mercury concentration in fish, namely 1 milligram per kilo, dry weight. In 10 300 of Sweden’s 83 000 lakes, this level is exceeded, making the fish unsuitable for human consumption. With a view to preventing the situation getting worse, the Swedes are seeking to cut mercury deposition by 80 per cent. Unfortunately, most of the mercury deposited in Sweden comes from other countries, so the Swedes are pressing for a pan-European strategy to reduce mercury emissions, comparable with that previously implemented for sulphur dioxide (Lindqvist, 1991a; Lindqvist, 1991b). In the Fifth Environmental Action Programme: Towards Sustainability, a European Community programme of policy and action in relation to the environment and sustainable development, several objectives are set. For mercury, the objective is a reduction in emissions of at least 70 per cent by 1995 (EC, 1993).

Sources of mercury emissions to the air include municipal waste incineration plants, coal-fired plants (Sloss, 1995) and municipal sewage sludge disposal plants (Carpi and Lindberg, 1997).

In 1992, an article by Slemr & Langer appeared in Nature, indicating that mercury concentrations in the atmosphere had increased as a result of anthropogenic emissions. The reported increase was greater in the Northern Hemisphere than in the Southern Hemisphere. The authors’ conclusions were based upon measurements carried out above the Atlantic Ocean in 1977, 1978, 1979, 1980 and 1990, from the southern tip of South America to Bremerhaven. There was apparently 6 000 tons of mercury, 92 per cent of it metallic, in the atmosphere. The average residence time of this atmospheric mercury was about one year, and three quarters of it had been released by human activity, in particular the combustion of coal (Slemr & Langer, 1992).

Mercury pollution is also causing considerable concern in the US.

Against this background, KEMA was asked by the Netherlands’ electricity generating companies to monitor the ambient atmospheric concentrations of various substances, including mercury, in Arnhem. The measurement technique used, which was based on active carbon, had previously been developed by KEMA itself. Monthly or bimonthly average values were obtained.

As well as measuring mercury levels, the concentrations of gaseous elemental arsenic, boron, bromine, antimony and selenium were also determined. During one of the measurement periods, iodine, fluorine and chlorine were also measured.