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1.
Influence of arsenic-bearing gold deposits on water quality in Zloty Stok mining area (SW Poland) 总被引:3,自引:2,他引:1
The Sudety Mountains contain polymetallic deposits which have been exploited since the Middle Ages. Distinct concentrations
of As, Hg, F, Cr in surface water near Zloty Stok suggested that groundwater in the area could also contain elevated metal
concentrations. Water samples from 15 locations including Zloty Stream, mine adit discharges, and selected springs generally
show low levels of dissolved components and near-neutral pH. However, arsenic concentrations range from 0.99 mg/l to 26.16 mg/l
at all 15 sample locations. Mercury concentrations were locally as high as 0.011 mg/l. These high arsenic and mercury concentrations
significantly exceed water quality standards and raise concerns for using Zloty Stream for potable water.
Recieved: 21 December 1998 · Accepted: 8 June 1999 相似文献
2.
Environmental impact of mining waste disposal on a tropical lowland river system: a case study on the Ok Tedi Mine, Papua New Guinea 总被引:3,自引:0,他引:3
The 1000 km long Ok Tedi/Fly River system receives about 66 Mt/year of mining waste from the Ok Tedi copper-gold porphyry
mine. Mine input has increased the suspended sediment load of the Middle Fly River about 5–10 times over the natural background.
A significant yet unknown amount of copper-rich material deposits unevenly in the extensive tropical lowland floodplain. Recent
alluvial sediments of the Fly River floodplain have copper contents of 620 mg/kg (±1σ: 430–900), whereas the regional background
is 40 mg/kg (±σ: 25–60). This pattern is mirrored and enhanced by the gold dispersal pattern with a 7 ppb Au background versus
a 140–275 ppb population in mine-derived material. Very high deposition rates (around 4 cm/y) of mine-derived sediment were
determined in locations close to the creeks and channels which link the Fly River with the outer floodplain. A thin layer
of 1–5 cm of copper-rich material (400–900 mg/kg Cu) was usually found on the bottom of drowned (tributary) valley lakes.
Average dissolved copper content in waters of the inner floodplain is around 9 μg/l (±1σ: 5–14) as compared to unpolluted
water from the outer floodplain with < 2 μg/l Cu. The present Fly River water, about 600 km downstream of the mine site, has
concentrations of 17 ± 3 μg/l dissolved Cu.
Received: 30 June 1996 / Accepted: 9 January 1997 相似文献
3.
Slovakia has many areas rich in thermal waters one of which is the Hornonitrianska kotlina depression. At four localities
three types of waters are found. The first belongs to the Ca–Mg–HCO3 type with T.D.S. 0.7 g/l, the second to the Ca–Mg–SO4 type with T.D.S. 1.37–2.01 g/l and the third to the Ca–Mg–SO4–HCO3 type with T.D.S. 0.97 g/l. Discharge at individual localities varies up to 30 l/s and temperatures of water reach 32.5–66.6 °C.
The waters are predominantly used for healing, rehabilitation purposes, recreation and heating.
Received: 8 March 1999 · Accepted: 7 June 1999 相似文献
4.
The Terme and Karakurt thermal resorts are located in the center of Kirşehir city in central Anatolia. Thermal waters with
temperatures of 44–60°C are used for central heating and balneologic purposes. Paleozoic rocks of the Kirşehir Massif are
the oldest units in the study area. The basement of the Massif comprises Paleozoic metamorphic schist and marbles which partly
contain white quartzite layers of a few tens of cm thickness. The metamorphic schists which are cut by granites of Paleocene
age are overlain by horizontally bedded conglomerate, sandstone, claystone, and limestone of upper Paleocene-Eocene age. Among
the thermal and cold waters collected from the areas of Terme and Karakurt, those from thermal waters are enriched with Ca–HCO3 and cold waters are of Ca–Mg–HCO3 type waters. The pH values of samples are 6.31–7.04 for the thermal well waters, 6.41 for thermal spring, 7.25 and 7.29 for
the cold waters, and 7.52 for the Hirla lake water. EC values are 917–2,295 μS/cm for the thermal well waters, 2,078 μS/cm
for thermal spring, and 471 and 820 μS/cm for the cold springs. The lowest TDS content is from water of T10 thermal well in
the Terme area (740.6 mg/l). The hot and cold waters of Terme show very similar ion contents while the Karakurt hot waters
at western most parts are characterized by distinct chemical compositions. There is ion exchange in thermal waters from the
T5 (5), T6 (6), T12 (7), and T1 (8) wells in the Terme area. The thermal waters show low concentrations of Fe, Mn, Ni, Al,
As, Pb, Zn and Cu. Waters in the study area are of meteoric origin, and rainwater percolated downwards through faults and
fractures, and are heated by the geothermal gradient, later rising to the surface along permeable zones. δ13CVPDB values measured on dissolved inorganic carbon in samples range from −1.65 to +5.61‰ for thermal waters and from −11.81 to
−10.15‰ for cold waters. Carbon in thermal waters is derived from marine carbonates or CO2 of metamorphic origin while carbon in cold waters originates from freshwater carbonates. 相似文献
5.
G. Stamatis 《Environmental Geology》1999,38(2):126-140
Peneos is the mainstream for the drainage of Thessaly's basin. It contributes significantly in recharging the aquifers, as
well as to the direct irrigation water, since there is intense agricultural activity in the basin of Thessaly. The investigation
of the hydrochemical conditions of the surface water system of Peneos showed that the chemical composition is related to the
lithology of the aquifers of the basin, the anthropogenic influence and the biological activity. The chemical composition
of this system changes in time and space. The salinity decreases during the winter period, in contrast to the summer period
when it increases drastically. The lower values of TDS appear in the upstream part of the river (95–124 mg/l) whereas downstream,
the values of TDS increase significantly (400–632 mg/l). The hydrochemical type Ca-Mg-HCO3 dominates the largest part of the river while it changes to NA-Cl in the estuary. The concentrations of the dissolved species
in the main Peneos river are higher than in the spring waters. Peneos is the most polluted river in Greece. The concentration
of the pollutants is higher at the downstream part of the river, but is lower than the accepted upper limits. The use of the
surface water of the system of Peneos river for irrigation purposes based on the SAR factor is acceptable because the absorption
ratio for Na and salinity are low and medium respectively.
Received: 27 October 1997 · Accepted: 21 September 1998 相似文献
6.
This paper presents a study on Manasbal lake, which is one of the high altitude lakes in the Kashmir Valley, India. Eighteen
water samples were analysed for major ions and trace elements to assess the variability of water quality of the lake for various
purposes. Geostatistics, the theory of regionalized variables, was then used to enhance the dataset and estimate some missing
spatial values. Results indicated that the concentration of major ions in the water samples in winter was higher than in summer.
The scatter diagrams suggested the dominance of alkaline earths over the alkali elements. Three types of water were identified
in the lake that are referred to as Ca–HCO3, Mg–HCO3 and hybrid types. The lake water was found to be controlled by rock–water interaction with carbonate lithology as a dominant
source of the solutes. The major (Ca2 + , Mg2 + , Na + , K + , NO3 and HCO3-{\rm{HCO}}_{3}^{-}, CO3 and Cl) and trace elements of the lake water were within the World Health Organization standards, therefore the lake water
was considered chemically safe for drinking purposes. Although NO3 concentration (ranging from 1.72 to 2 mg/L), is within the permissible limit and not very alarming, the gradually increasing
trend is not acceptable. It is however, important to guard its spatio-temporal variability as the water is used for domestic
as well as agricultural purposes. This study is significant as hydrogeological information on such high altitude lakes in
India is scanty. 相似文献
7.
Improvement of groundwater quality due to fresh water ingress in Potharlanka Island, Krishna delta, India 总被引:1,自引:0,他引:1
Hydrochemical study had been carried out on the groundwater resources of Potharlanka Island, Krishna delta, India. Groundwater
samples were collected and analyzed at 42 sites in December 2001 and October 2006. A comparative study of hydrochemical data
indicates: groundwater is mildly alkaline with a pH of 7.0–8.2; electrical conductivity (EC) varies from 605 to 5,770 μS/cm
in December 2001, and 652–5,310 μS/cm in October 2006. More than 62% of the groundwater samples in 2006 have TDS value <2,000 mg/l,
which is within permissible limit of potable water, but 57% of the samples in 2001, are higher than the maximum permissible
limit. Extremely low HCO3/Cl and variable high Mg/Ca (molar ratios) had been indicated the transformation of the fresh groundwater aquifer systems
to saline in 2001. Groundwater of this Island is mainly classified as Na–Cl and mixed types. A high percentage of Na–Cl type
of these waters indicates the possibility of seawater ingression/intrusion process during 2001 and comparatively mixed water
type indicates the dilution activities of groundwater. Excessive withdrawal of groundwater has caused the increase of saline
water intrusion. Improvement of groundwater quality in this Island due to artificial recharge structures made by NGRI under
RGNDWM project and affects of the flood due to heavy rainfall of the months of September–October 2005 are discussed in this
paper. 相似文献
8.
L. A. Shevenell 《Environmental Geology》2000,39(7):807-815
Within the next 10–15 years, over 35 mines in Nevada will have a lake in their open pit mines after dewatering and cessation
of mining. Of the ten past or existing pit lakes at eight different gold mines for which temporal data are available, most
had near neutral pH, yet most had at least one constituent (e.g., As, SO4, TDS) that exceeded drinking water standards for at least one sampling event. Most samples from pit lakes had TDS exceeding
drinking water standards, but lower than that in the natural Pyramid (TDS≈5,500 mg/l) and Walker (TDS≈14,000 mg/l) Lakes.
In the past century, salinity increased in both natural, terminal lakes, in part due to irrigation withdrawals and evapoconcentration.
The salinity in the pit lakes may also increase through time via evapoconcentration. However, water balance models indicate
that up to 132% (Walker Lake) of the total yearly inflow evaporates from the terminal lakes, whereas steady-state may be reached
in the pit lakes modelled, where evaporative losses account for only ≈6% of the total pit lake volume annually and ≈100% of
the net inflow (groundwater inflow minus outflow, precipitation and runoff into the lake). The effects of evapoconcentration
are expected to be less significant at most pit lakes than at the natural, terminal lakes because (1) evaporation rates are
lower at many pit lakes because they are located at higher elevations than the terminal lakes, and (2) the surface area to
depth ratio of the pit lakes is >1000 times smaller than that of the terminal lakes.
Received: 1 March 1999 · Accepted: 13 April 1999 相似文献
9.
Yangtze Delta, China: Taihu lake-level variation since the 1950s, response to sea-level rise and human impact 总被引:1,自引:0,他引:1
Hydrological records collected from water gauge stations since the 1950s demonstrate that the Taihu lake level is rising.
The average rate of the lake-level rise is 0.4–1.1 mm/year during the non-flood season, resulting directly from a rise in
sea level. High rates of 3.0–5.0 mm/year of rise are even recorded during the wet season. This indicates increasing human
activities such as reclamation, sluicing and embanking, which significantly hinder the expulsion of extra lake water to the
coast shortly after a rainfall. Generally, the lake level of the western inlet is higher than that of the eastern outlet.
However, the lake-level difference between the west and east has been diminished annually from ∼10–15 cm in the 1950s to <3 cm
at the present time. During non-flood seasons, the lake-level difference even appears to be reversed, indicating a retrogression
of the lake flow from east to west. It is predicted that the Taihu drainage basin will lose much of its natural water-expelling
ability in the next 50 years as the sea level continues to rise, and retrogression will likely occur during the flood season
in the near future.
Received: 13 March 1998 · Accepted: 21 July 1998 相似文献
10.
Arsenic in mine waters: an international study 总被引:4,自引:4,他引:4
M. Williams 《Environmental Geology》2001,40(3):267-278
Hydrochemical data are presented for arsenic (As) in the mine waters of 34 gold and base-metal mining localities in seven
countries of south-east Asia, Africa and Latin America, encompassing contrasting climatic settings and at least eight discrete
styles of primary mineralization. Peak dissolved As concentrations at these sites range from 0.005–72 mg/l, with the United
States Environmental Protection Agency (US-EPA) potable water threshold of 50 μg/l exceeded in 25 cases. Arsenate (As5+) constitutes the dominant species at over 80% of sites. Very high dissolved As concentrations (>1 mg/l) show no systematic
between-site relationship with mine water pH/Eh regime. Important determinants of mine water As fluxes include iron hydrochemistry,
the presence of cyanic ore processing effluents, site geology, the paragenetic sequence that follows sulphide oxidation, climate
and mine management. Human toxicological impacts of As contamination have been recognized at only one case-study site, with
a further four considered to warrant more detailed risk assessment.
Received: 2 November 1999 · Accepted: 21 March 2000 相似文献
11.
C. B. Dissanayake A. M. Rohana Bandara S. V. R. Weerasooriya 《Environmental Geology》1987,10(2):81-88
The Kandy lake, situated in the heart of Sri Lanka's second largest city with a population of nearly 120,000, has been monitored
to probe the extent of heavy metal pollution. Although the lake is a source of drinking water to the city, a large number
of effluent canals drain into the lake carrying a continuous flow of industrial and domestic waste matter. A total of 66 surface
water samples were analyzed for their Fe2+, total Fe, total V, SO
4
2−
, Cd2+, and Pb2+ contents. Pb and Cd were found in high concentrations averaging 150 μg/l and 77 μg/l, respectively, and exhibit a marked
positive correlation with each other (r=+0.94). Vehicular emissions and industrial waste matter contribute largely to the Pb and Cd contents of the lake, the anthropogenic
influence outweighing the contributions made by geological materials. All field observations and laboratory experiments indicate
a tendency of the Kandy Lake towards eutrophicity. 相似文献
12.
A hydrogeochemical survey was conducted on Pico Island (Azores archipelago) in order to evaluate the groundwater chemistry
patterns and the main mineralization processes. Samples were from cold waters and corresponded mainly to sodium chloride type.
Conductivity measurements were ∼82–9790 μS/cm and suggest the existence of highly mineralized waters. In fact, 18% had a conductivity
>5130 μS/cm and the total dissolved solid (TDS) value for two of the wells was from the brackish water range. The changes
in groundwater composition are because of two main processes: (1) silicate mineral dissolution, especially in a few springs
located at high altitude and (2) water salinization in the coastal area, as a result of saltwater intrusion and sea-salt spraying.
The salinization process corresponds to a binary mixing system, as suggested by the chloride and δ18O data, and explains the sharp concentration increase in major and minor species detected in several wells.
Received: 23 July 1999 · Accepted: 8 December 1999 相似文献
13.
The hydroelectric reservoir of Petit Saut, French Guiana, was created in 1994–1995 by flooding 350 km2 of tropical forest. When sampled in 1999, the lake exhibited a permanent stratification separating the 3–5 m thick, oxygenated
epilimnion from the anoxic hypolimnion. The rate of anaerobic organic carbon mineralization below the oxycline was on the
order of 1 μmol C m−2 s−1 and did not show a pronounced difference between wet and dry seasons. Methanogenesis accounted for 76–83% of anaerobic carbon
mineralization, with lesser contributions of sulfate reduction and dissimilatory iron reduction. Upward mixing of reduced
inorganic solutes explained 90% of the water column O
2 demand during the dry season, while most O
2 consumption during the wet season was coupled to aerobic respiration of organic matter synthesized in the surface waters.
Inorganic mercury species represented 10–40% of total dissolved mercury in the epilimnion, but were of relatively minor importance
(≤10%) in the anoxic portion of the water column. Net production of soluble organic mercury compounds in the flooded soils
and anoxic water column did not vary significantly between wet and dry seasons. Methylmercury accounted for about 15% of total
dissolved mercury below the oxycline. Its estimated net production rate, 0.04 mg m−2 yr−1, is of the same order of magnitude as values reported for contaminated lakes and flooded terrestrial ecosystems. 相似文献
14.
Hydrogeochemical and isotopic investigation of the Bursa-Oylat thermal waters, Turkey 总被引:1,自引:1,他引:0
Suzan Pasvano?lu 《Environmental Earth Sciences》2011,64(4):1157-1167
The Oylat spa is located 80 km southeast of Bursa and 30 km south of Ineg?l in the Marmara region. With temperature of 40°C
and discharge of 45 l/s, the Oylat main spring is the most important hot water spring of the area. Southeast of the spa the
Forest Management spring has a temperature of 39.4°C and discharge of 2 l/s. The G?z spring 2 km north of the spa, which is
used for therapy of eye disease, and cold waters of the Saadet village springs with an acidic character are the further important
water sources of the area. EC values of Main spring and Forest Management hot spring (750–780 μS/cm) are lower than those
of Saadet and G?z spring waters (2,070–1,280 μS/cm) and ionic abundances are Ca > Na + K > Mg and SO4 > HCO3 > Cl. The Oylat and Sızı springs have low Na and K contents but high Ca and HCO3 concentrations. According to AIH classification, these are Ca–SO4–HCO3 waters. Based on the results of δ18O, 2H and 3H isotope analyses, the thermal waters have a meteoric origin. The meteoric water infiltrates along fractures and faults,
gets heated, and then returns to surface through hydrothermal conduits. Oylat waters do not have high reservoir temperatures.
They are deep, circulating recharge waters from higher enhanced elevations. δ13CDIC values of the Main spring and Forest Management hot spring are −6.31 and −4.45‰, respectively, indicating that δ13C is derived from dissolution of limestones. The neutral pH thermal waters are about +18.7‰ in δ34S while the sulfate in the cold waters is about +17‰ (practically identical to the value for the neutral pH thermal waters).
However, the G?z and Saadet springs (acid sulfate waters) have much lower δ34S values (~+4‰). 相似文献
15.
Human impacts in Antarctica: trace-element geochemistry of freshwater lakes in the Larsemann Hills, East Antarctica 总被引:2,自引:1,他引:2
Fresh water lakes are found in basement rock basins in the Larsemann Hills, East Antarctica, during the summer months. These
lakes constitute a relatively simple natural laboratory to investigate the effects of recent and well-documented anthropogenic
impact on a “pristine” environment. Larsemann Hills freshwaters have extremely low salinity (typically <1‰), and contain very
low concentrations of trace elements of environmental significance such as Pb, U, and Zn. Typical Pb concentrations range
from less than 5 ppt to 250 ppt. Although trace metal concentrations appear to be higher in lakes situated in the vicinity
of stations, they are consistently lower (by several orders of magnitude, for some elements) than Standard International Drinking
Water Guidelines. The chemistry of the lake waters is dominated by sea-spray input. Consequently, it is primarily a function
of geographical factors, such as distance from the shore and exposure to winds. Shallow-level groundwater and surface water
also contribute to the lake chemistry. No evidence was found for contamination from global air circulation. Although contamination
resulting from activities at the research stations is generally near or below detection levels, very low levels of trace metal
anthropogenic contamination were found in the vicinity of some research stations.
Received: 13 November 1998 · Revised: 23 March 1999 Accepted: 12 April 1999 相似文献
16.
Heavy metals in sediments of a large, turbid tropical lake affected by anthropogenic discharges 总被引:2,自引:0,他引:2
Bottom-water data and trace metal concentration of Cu, Cr, Ni, Pb, Co, Zn, and organic matter in surficial sediment samples
from 13 sampling stations of Lake Chapala in Mexico were studied. The lake is turbid with a great amount of flocculated sediments
as a result of wind mixing, sediment re-suspension, and Lerma River discharges. Al distribution pattern in sediments was used
as an indicator of the Lerma River discharges into Lake Chapala. The highest values of Cu (33.27 ppm), Cr (81.94 ppm), Pb
(99.8 ppm), and Zn (149.7 ppm) were detected in sediments near the lake outlet. The bioavailable metal fraction is low for
all metals except Pb, which shows 65–93% of the total metal concentration in bioavailable form. The minimum energy zone in
the lake was related to organic matter concentration and was located in the SE part of the lake. An analysis of the studied
parameters shows two zones: eastern zone (fluvio-deltaic) and central-western zone (lacustrine).
Received: 9 September 1998 · Accepted: 16 November 1998 相似文献
17.
A baseline study involving analyses of surface and subsurface water samples from the Akpabuyo area was carried out in order
to assess their suitability for drinking, domestic and agricultural purposes. Study results show that the waters are acidic
(3.41≤pH≤6.28), soft (hardness 2.09–10.68 mg/l as CaCO3), fresh (conductivity <1400 μs/cm) and characterised by low sodium adsorption ratio, SAR (0.08–0.59). In addition, the mean
values of the major cations (Ca2+, Mg2+, Na+, K+) and anions (SO4
2–, Cl–, HCO3
–) are all within the World Health Organisation (WHO) standards. Taking all this into consideration (except pH), the waters
may be regarded as excellent for drinking, domestic and agricultural purposes. On the basis of regression equations, the major
cations (K, Na, Ca, Mg) correlate well with conductivity. Finally, results also show that four chemical facies are delineated.
These include Ca-Cl, Na-Cl, Ca-SO4 and Ca-HCO3.
Received: 19 June 1996 / Accepted: 15 April 1997 相似文献
18.
Foresighted and determined local authorities, purposeful exploration (i.e. by seismic reflection) and extensive testing led
to the discovery of a substantial groundwater resource near the community of Seon (Switzerland) at a depth of 268–305 m. Production
tests revealed a hydraulic conductivity of ∼5.10–5 m/s, transmissivity of ∼5.10–4 m2/s and a storage coefficient of ∼2% in the aquifer. Pumping up to 1500 l/min is sustainable; the water quality complies chemically
and bacteriologically with drinking-water requirements. The residence time of several 103 years, determined by isotope techniques, guarantees protection from surface contamination. The elevated temperature of 19.5 °C
of the produced water enables combined use for drinking water and space heating. The environmental benefits are substantial:
the emission reduction amounts up to 780 tons/year CO2 and 1 ton/year SO2.
Received: 21 September 1998 · Accepted: 10 February 1999 相似文献
19.
The CO2-rich thermal groundwater in the Betic Cordilleras in Spain has been studied with regard to the geological and hydrogeological
setting, physical and chemical characteristics, and 13C-isotope content. The study area is about 60 km northeast of Almería city, in southeastern Spain. The thermomineral waters
are plentiful and are related to regional geothermal anomalies. Temperatures of 20 −41°C, high bicarbonate concentrations
(183–1824 mg/L), and high amounts of PCO2 (<1.1 bar) characterize the groundwater. CO2 spatial variations are related to proximity to the Carboneras, Palomares, and Guadalentín fault systems, which may be the
surface representation of the zone of crustal thinning and magmatism. δ
13C values probably indicate a deep source for the CO2, either the mantle or perhaps carbonate rocks in the metamorphic substratum. The high amount of CO2 in the groundwater causes problems in wells and severely restricts water usage. The hydrothermal features of this area are
probably related to neotectonic activity.
Received, September 1998/Revised, June 1999, September 1999/Accepted, December 1999 相似文献
20.
The Malter Reservoir is situated about 30 km south of Dresden (eastern Germany) in a historical mining area of the eastern
Erzgebirge. It was built in 1913 for the protection from floodwaters, droughts and for generating electricity. The river Rote
Wei?eritz is the main source of clastic input into the lake. Geochemical and sedimentological data of gravity-and piston-cores,
recovered from the deepest point of the lake, document the environmental history of the drainage area since 1963. 137Cs dating gives an average sedimentation rate of ∼2.9 cm/year. Within the whole core, heavy metals are strongly enriched (parentheses
refer to enrichment factors as compared with average shale): cadmium (290), silver (140), bismuth (90), antimony (25), lead
(21), zinc (14), tin (13), uranium (9), tungsten (9), molybdenum (5), copper (4), thallium (3) and chromium (2). Enrichments
are detectable for the whole registered time-period of 81 years. Peaks of up to 27 mg/kg silver, 37 mg/kg bismuth, 91 mg/kg
cadmium, 410 mg/kg chromium, 240 mg/kg copper, 20 mg/kg molybdenum, 14000 mg/kg phosphorus, 740 mg/kg lead, 6,5 mg/kg antimony,
74 mg/kg tin, 52 mg/kg tungsten and 1900 mg/kg zinc reflect local events caused by human impact. Inputs from different pollution
sources at different times are represented by highly variable elemental concentrations and ratios within the core. High pH
values within the water and the sediment column, the large adsorption capacity of the fine-grained Corg.-rich sediment, and the presence of low Eh-values and sulphide ions in the sediment prevent the remobilisation of the toxic
elements. Erosion of these contaminated sediments during floods, channel flows or resuspension during removal of the sediments
may lead to a downstream transfer of pollutants. Contents of P and Corg., as well as diatom abundance, indicate a change from oligotrophic to eutrophic conditions in the lake during ∼1940–1950.
This was mainly caused by high agricultural activity in the drainage area. Reduced contents of Cu, Zn, Cd and Cr since the
reunification of East and West Germany are obviously caused by increasing environmental protection measures, such as wastewater
purification and especially the closing of contaminating industries.
Revision received: 23 September 1999 · Accepted: 17 December 1999 相似文献