Authors: Williamson B J, Purvis O W, Bartok K*, Har N**, Manolache E**, John D M, Stanley C J and Vlad N S***Biological Research Institute, Str. Republicii 48, 3400 Cluj-Napoca, Romania **Babes-Bolyai University, 1 Kogalniceanu Str., 3400 Cluj-Napoca, Romania
Thousands of years of mining and minerals processing in the Apuseni Mountains of Romania have caused severe environmental damage with important consequences for human and environmental health. These effects are particularly serious where the minerals industry is in close proximity to urban environments. In the town of Zlatna, in the Apuseni Mountains of Romania, a minerals processing plant and smelter are located within two minutes' walk of the town centre. Gaseous emissions (SO2, NOX) and fall-out of particles enriched in Pb, Zn, Cu and Cd cause acid precipitation and heavy metal contamination for more than 30 km down-wind from the smelter. Severe health problems in local communities were first reported over 15 years ago (Suciu, 1981). A subsequent environmental health study by the US Agency for International Development (USAID) identified high blood Pb levels in local children of up to 70 ug/dL and a marked increase in the incidence of chronic bronchitis due to high levels of SO2 (Billig et al., 1999). Lead shows neurotoxic effects in children when blood levels exceed 10 ug/dL (US Centre for Disease Control and Prevention).
Smelter chimneys over Zlatna
There are no immediate low cost solutions to prevent further contamination short of moving the town, closing down the plant and carrying out a major soil clean-up programme. Any such measures are unlikely given the depressed state of the local economy and that the smelter is the main employer in the area.
In order to devise long-term solutions to the problems caused by environmental contamination, the processes of mineral breakdown, the biogeochemical mobilisation of toxic metals, the mechanisms and extent of bioaccumulation, and consequent transport via the food chain must be understood. Initial studies are being undertaken by a multidisciplinary team from The Biological Research Institute and Babes-Bolyai University, Cluj, and The Natural History Museum, London, UK
Signpost at the entrance to Zlatna warning: 'Beware of pollution -the forest is dying'
Smoke emissions from the smelter often sink to the valley floor enveloping the town in a heavy sulphurous mist which is occasionally accompanied by fall-out of ash containing particles rich in metals. This results in extremely high soil lead levels on the valley sides of between 50 and 4,000 ppm (Gurzau et al., 1995). Limited studies on metal accumulation in different types of soils have shown that lead is most strongly accumulated in the uppermost 'brown earth' horizon of forest soils (Preda et al., 1988). This behaviour is not common to all metals, with cadmium, another extremely toxic metal, showing highest concentrations in agricultural soils (Preda et al., 1988). Despite lead being apparently less abundant in agricultural soils, locally grown vegetables may still contain high concentrations. Turnips, cabbages and grass, for example, have been found to contain 536 ppm, 347 ppm and 1,971 ppm lead respectively (Zahan et al., 1981), largely dependent on soil type (Keul et al., 1984). The European Commission (III/5125/95 Rev. 3) has set maximum limits on lead in cereals, fruit and vegetables of less than 0.3 ppm.
Aerial pollution from the smelter also has a major impact on the mixed deciduous woodland of the area which is dominated by beech (Fagus sylvatica), hornbeam (Carpinus betulus) and oak (Quercus petraea) (eg Keul et al., 1984). Forest soils are highly acidic, down to pH 2 (Bartok, 1982). On the valley sides, 'down-wind' of the smelter, tree and herbaceous plant cover is sparse and appear's to show severe damage from sulphur dioxide and acid rain. Most of the trees show extensive necrosis, the dying off of upper canopy branches, the blackening of their trunks, and, by mid July, the yellowing of leaves. The lack of vegetation on many of the steeper slopes has led to severe soil erosion. On more gentle slopes, leaf litter on the forest floor is extremely deep (up to 60 cm) due to the reduction in abundance of microfaunal organisms, such as nematodes, which usually cause its decomposition (Popovici, 1981). Beech woodland around Zlatna contains only 27% of the number of earthworms found in similar, less contaminated ecosystems 30 km from the town (Pop, 1987). The reduction in abundance of invertebrates has led to a marked decrease in the number of organisms higher up the food chain including birds (Munteanu, 1982). Among the most successful organisms on the forest floor are fungi, including the edible mushroom Macrolepiota procera. However, these have been shown by Pop and Nicoara (1996) to contain thirteen times the Cd and four times the Pb levels permitted by World Health Organisation health security standards, with young fruit bodies containing the highest levels.
Lichens, which consist of a fungus and an alga living together, are commonly used as biomonitors of air pollution, including SO2 levels, Pb from car exhausts, radionuclide fall-out from Chernobyl and metal-bearing dusts from mining activities (see Garty, 1993). Lichens lack a protective outer cuticle and may therefore absorb metals to several weight percent (Purvis, 1996). The Zlatna area is so polluted that only the most tolerant crust-like lichens are present. For monitoring purposes, Bartok (1982, 1988) found that it was necessary to transplant lichens into the area from uncontaminated sites. The lichen Parmelia conspersa was found to accumulate up to 2,500 ppm lead over a 12 month period. Not surprisingly, accumulation was species dependent and correlated with distance from the polluting source. A slight improvement in air quality was noticed over a five year period as a result of the installation of a new, much higher smelter chimney. This study demonstrated the use of lichens in monitoring the effectiveness of environmental initiatives to reduce polluting emissions.
Current studies have focused on the mechanisms of bioaccumulation of lead by the crustose lichen Acarospora smaragdula (Purvis et al., 1999) [Request a reprint]. The presence of secondary Pb precipitates within specific regions of the lichen, formed as a result of the breakdown of primary smelter particulates, indicates that Pb is highly mobile under the prevailing acidic conditions. The remarkable ability of Acarospora smaragdula to survive under such conditions and to accumulate Pb and other metals suggests that this lichen may provide a useful bioindicator of aerial particulate contamination in polluted areas where macrolichens are usually absent.
Local streams and the main Ampoi river receive contaminated water in the form of acid, and occasionally highly alkaline, smelter effluent and metal-enriched acid leachates from the roughly 1 km2 tailing heaps around the processing plant. In some areas these drain directly into local agricultural land. Acid leachates (pH 3.7 to 4), collected in April 1996, were found to contain 4 ppm Pb, 1,100 ppm Zn and 4 ppm Cd. This compares with US Environmental Protection Agency limits for drinking water of 0.005 ppm, 5 ppm and 0.015 ppm, respectively. The acid nature of the leachates is due to the breakdown of sulphide minerals, particularly iron pyrite (FeS2) and galena (PbS), which remain in the tailings due to inefficient extraction in the processing plant. Sulphur is released in the form of sulphate, which dissolves to produce weak sulphuric acid in which potentially toxic elements are more soluble. The evaporation of the leachates has led to the formation of strangely beautiful crusts of sulphur and copper sulphate crystals over wide areas of the tailings heaps. Copper sulphate solutions have formed in standing water, and these have reacted with scrap iron to produce a coat of gleaming native copper.
Spoil heaps around Zlatna
Mixing of heavy metal-enriched acid leachates with local groundwaters commonly results in the formation of a blanket of red-brown Fe-hydroxides on stream beds. This is because regional groundwaters have a naturally high pH of around 7.3 due to much of the local sedimentary rock containing carbonate. The sudden increase in pH causes the rapid hydrolysis of Fe from solution. Whether the more toxic metals such as Cu, Pb and Cd are adsorbed to the surfaces of the Fe-hydroxides or are carried off in solution has yet to be established and may have important implications for developing remediation systems in the area. Removal of metals by adsorption to Fe-hydroxides is commonly used in the remediation of acid mine drainage, for example from the abandoned Wheal Jane tin mine in Cornwall, UK (Robb and Robinson, 1995).
A well-known feature of heavy metal polluted waters is a low biotic diversity with the survival in abundance of just a few pollution-tolerant species. Many algae can accumulate high levels of heavy metals within their cells, or as amorphous and mineral precipitates on their surface. Such accumulation has important environmental implications since algae are the principal primary producers in many aquatic food chains. There has been little research on metal accumulation by algae or their tolerance to low pH in Romania apart from laboratory-based physiological studies of cultured strains of green algae and cyanobacteria (see Dragos, 1980; Nagy-Tóth and Barna, 1982). In heavy metal-rich leachates of neutral pH draining from the Zlatna tailings heaps, there are growths of Plectonema boryana. This cyanobacterium is well known to be tolerant of heavy metals (see Kelly, 1988) and has a texture similar to that of cellophane due to the presence of firm, colourless sheaths which surround its numerous microscopic filaments. Plectonema is known to accumulate copper, lead and other metals as polyphosphate bodies in which form the alga is thought to be protected from the toxic effects of the metals (see Jensen et al., 1986). The identification of species which accumulate metals and grow under different environmental conditions is important in developing their use in remediation technologies. The possibility exists of genetically engineering species particularly suited for this purpose.
The town of Zlatna is just one of many in Europe suffering the effects of decades of chronic industrial pollution. Worldwide, the twentieth century has become synonymous with the sight of smoking chimneys, slag heaps, rubbish tips, illegal dumps and 'contaminated land'. Almost all of the planet's surface is contaminated to some degree by metals and other toxic substances. But does metal contamination necessarily lead to environmental degradation? This depends on the type of metals present, their concentration and their bioavailability. The bioavailability of different metals is poorly understood, being not only dependent on which organisms are present but on a wide range of environmental variables. A better understanding is important not only in conserving natural habitats but also for protecting human health as metals may be accumulated/concentrated through the food web. Low cost solutions to the problems of metal contamination are therefore urgently required. To be universally acceptable, these solutions must not adversely affect local economies or threaten jobs. Natural remediation systems are likely to provide the most cost effective long-term solutions.
The survival of organisms in the presence of toxic metals in contaminated sites such as Zlatna depends on intrinsic biochemical, physiological and genetic properties. While it is certainly true that Zlatna has suffered intense environmental degradation, the area is also a natural laboratory for studying fundamental processes of metal mobilisation and bioaccumulation. Our studies are designed to both identify risk to human health and for working towards better natural systems for cleaning-up such metal contaminated environments.
The authors wish to thank the British Council and the Royal Society for funding, and Vic Din for technical help.
For further information contact:Dr Ben Williamson or Dr William Purvis