Introduction

This section includes pollutants singled out for control under recent international protocols extending the Convention on Long-range Transboundary Air Pollution- namely Persistent Organic Pollutants (POPs) and Heavy Metals (HMs).

The UN/ECE Protocol on Persistent Organic Pollutants focuses on a list of 16 substances (or groups of substances), which have been identified according to certain risk criteria. In brief, these 16 pollutants may be classified in three source sectors as follows:

1. Pesticides: aldrin, chlordane, chlordecone, DDT, dieldrin, endrin, heptachlor, hexachlorobenzene (HCB), mirex, toxaphene, hexachlorocyclohexane (HCH) (incl. lindane);
2. Industrial Chemicals: hexabromobiphenyl, polychlorinated biphenyls (PCBs);
3. By-products or Contaminants: dioxins, furans, polycyclic aromatic hydrocarbons (PAHs).

The ultimate objective of the protocol is to eliminate any losses, discharges and emissions of POPs to the environment. This is achieved through several different legislative mechanisms. First, the production and use of several compounds is banned (aldrin, chlordane, chlordecone, dieldrin, endrin, hexabromobiphenyl, mirex and toxaphene). Secondly, several compounds are scheduled for elimination at a later date (DDT, heptachlor, hexachlorobenzene, PCBs). Finally, the protocol severely restricts the use of selected compounds (DDT, HCH- including lindane and PCBs). Limited uses which are thought to be essential and for which there are no adequate substitutes, can be exempted. For instance, the use of substances like DDT would be allowed under the protocol for public health emergencies. The protocol includes provisions for dealing with the surplus of products that will be banned.

Under the protocol, countries are also required to reduce their emissions of dioxins, furans, PAHs and HCB below their levels in 1990 (or an alternative year between 1985 and 1995). The protocol requires the best available techniques (BAT) to be applied to cut emissions of these POPs. For the incineration of municipal, hazardous and medical waste, it lays down specific limit values. The protocol allows for the addition of further compounds into control, depending on the development of the scientific basis for such an action.

During 1999 EPAQS published a report on PAHs which recommended an Air Quality Standard of 0.25 ng m^-3 benzo[a]pyrene as an annual average. As a result, further work assessing the concentrations of PAHs in the atmosphere has been commissioned by DEFRA and the results compared with the spatially disaggregated emissions inventory.

Extensive improvements have been made in compiling the 1998 UK emission estimates for POPs. This has been instigated in a response to the increasing interest in hazardous air pollutants and their impact on the environment over the last several years. The level of data available for many of these pollutants is relatively limited and hence several areas of the current emission inventory have been targeted for improvements which will be included in future emission estimates as a part of the NAEI continuous improvement process. Particular improvements included in the 1998 inventory are a larger data source, and significant advances in the speciation of pollutant groups.

Table 6.1 lists the toxic pollutants (i.e. POPs and heavy metals) included in the current inventory together with their total UK emissions in 1998. Each of the pollutant classes are considered in more detail in the following sections.

The UN/ECE Protocol on Heavy Metals targets three particularly harmful substances: lead, cadmium and mercury. Countries are obliged to reduce their emissions of these three metals below their levels in 1990 (or an alternative year between 1985 and 1995). The protocol aims to cut emissions from industrial sources (iron and steel industry, non-ferrous metal industry), combustion processes (power generation, road transport) and waste incineration.

The protocol specifies limit values for emissions from stationary sources and requires BAT for obtaining emission reductions from these sources, such as special filters or scrubbers for combustion sources or mercury-free processes. The protocol also requires countries to phase out leaded petrol.

Under the protocol, measures are introduced to lower heavy metal emissions from other products e.g. mercury in batteries, and examples are given of management measures for other mercury-containing products, such as electrical components (thermostats, switches), measuring devices (thermometers, manometers, barometers), fluorescent lamps, dental amalgam, pesticides and paint.

Further metals may be added to the protocol, and further measures may be introduced for lead, cadmium and mercury, depending on the development of the scientific basis for action.

The best known effects of heavy metals are those on humans and animals. Of these, the most important effects are deterioration of the immune system, the metabolic system and the nervous system. They lead to disturbances in behaviour and some heavy metals are suspected to be or have been proven to be carcinogenic.

The impact of heavy metals on the environment due to long-range transport can be summarized as:

1. Impact on aquatic ecosystems. Atmospheric deposition of metals may influence the quality of surface waters and ground water. In addition to the effects on the uses of water (e.g. restricted use of water for human consumption, livestock, recreation etc) accumulation in aquatic organisms may have adverse effects on the food web.
2. Impact on terrestrial systems. Metal uptake by plants is a key route for the entry of metals into the food chain. Contaminants may be toxic to plants and can alter the structure or diversity of a habitat. When plants accumulate metals, these can be ingested by animals creating the potential for toxic effects at higher trophic levels.
3. Mesofauna and macrofauna. The accumulation of cadmium and lead in birds and mammals in remote areas is attributable to long range atmospheric transport.
4. Agricultural products. Airborne heavy metals accounts for significant fractions of the total heavy metal input to arable soils.

Major environmental problems due to long range transport have been reported, relating to the:

• Accumulation of Pb, Cd and Hg in forest top soils, implying disturbed nutrient recirculation in forest ecosystems and increased stress on tree vitality in central Europe, reinforced by the acidification of soils
• Highly increased content of Hg in fish from lakes, especially in Scandinavia.