Baseline element concentrations in soils and plants,Wattenmeer National Park,North and East Frisian Islands,Federal Republic of Germany

Baseline element concentrations are given for dune grass (Ammophilia arenaria), willow (Salix repens), moss (Hylocomium splendens) and associated surface soils. Baseline and variability data for pH, ash, Al, As, Ba, C, Ca, Cd, Ce, Co, Cr, Cu, Fe, Hg, K, La, Li, Mg, Mn, Na, Nb, Nd, Ni, P, Pb, S, Sc, Se, Sr, Th, Ti, V, Y, Yb, and Zn are reported; however, not all variables are reported for all media because, in some media, certain elements were below the analytical detection limit. Spatial variation in element concentration between five Frisian Islands are given for each of the sample media. In general, only a few elements in each media showed statistically significant differences between the islands sampled. The measured concentrations in all sample media exhibited ranges that cannot be attributed to anthropogenic additions of trace elements, with the possible exception of Hg and Pb in surface soils.     

Determining baselines and variability of elements in plants and soils near the Kenai National Wildlife Refuge,Alaska

Recent investigations on the Kenai Peninsula had two major objectives: (1) to establish elemental baseline concentrations ranges for native vegetation and soils; and, (2) to determine the sampling density required for preparing stable regional geochemical maps for various elements in native plants and soils. These objectives were accomplished using an unbalanced, nested analysis-of-variance (ANOVA) barbell sampling design. Hylocomium splendens (Hedw.) BSG (feather moss, whole plant), Picea glauca (Moench) Voss (white spruce, twigs and needles), and soil horizons (02 and C) were collected and analyzed for major and trace total element concentrations. Using geometric means and geometric deviations, expected baseline ranges for elements were calculated. Results of the ANOVA show that intensive soil or plant sampling is needed to reliably map the geochemistry of the area, due to large local variability. For example, producing reliable element maps of feather moss using a 50 km cell (at 95% probability) would require sampling densities of from 4 samples per cell for Al, Co, Fe, La, Li, and V, to more than 15 samples per cell for Cu, Pb, Se, and Zn.     

Fluctuations of element concentrations during the growing season of Polytrichum formosum (Hedw.)

Fourteen elements (Al, Ba, Ca, Cd, Cr, Cu, Fe, K, Mg, Ni, Pb, Sr, Ti, and Zn) were quantitatively determined by AES/ICP in aboveground parts of the endohydric moss Polytrichum formosum (Hedw.) after sampling over regular intervals from 1985 to 1987. With the exception of K, Mg, and Zn all elements showed a large continuous fluctuation (> 30%) during the growing season. Four different patterns of seasonal variation were found: (1) large seasonal variations of element concentrations (～80%) with maximum concentrations in winter and lowest concentrations in the summer months (Al, Fe, Cr, Mg, Pb, and Ti), (2) smaller seasonal variations (～50%) with maximum concentrations in winter and lowest concentrations in summer (Ba, Ca, Cd, Cu, Sr), (3) slight seasonal variations (～30%) with maximum concentrations in the summer (K), and (4) slight seasonal changes (～30%) with maximum concentrations in the winter (Mg and Zn). The relative biological variance of element concentrations between 9 different stands of Polytrichum formosum decreases in the following sequence: Ti, Al, Pb, Fe, Cr, Ni, Ba, Ca, Cu, Cd, K, Mg, Sr, Zn. The relative biological variance of individual elements is generally lower than the variance in element concentrations caused by seasonal changes. Because of its high biological variance for most elements investigated (seasonal as well as between different stands of Polytrichum formosum) this moss should only be used as a passive bioindicator, if all other environmental parameters are standardized.     

Uptake of nutrients and heavy metals by pine trees under atmospheric pollution

Pollution-induced changes in concentrations of elements in pine needles, branches, stem bark, and wood were investigated on 12 plots along the pollution gradient at distances of 5 to 77 km from the Pechenganikel copper-nickel smelter on the Kola Peninsula (northwestern Russia), the largest emitter of sulfur and heavy metals in northern Europe. Close to the pollution source, concentrations of S, Ni, Cu, Pb, and Cd in all the pine compartments were higher as compared to their background levels, while the Zn concentrations were lower. The concentrations of Ni and Cd—the main metals emitted—were the highest in all the pine compartments. Age-related variations in the needle composition were comparable to those at the background plots. Branches and, especially, stem bark, were richer in heavy metals than other tissues and, in addition to wood, contributed significantly to the accumulation of metals in the biomass of the polluted pine forests. Changes in the chemical composition of plant tissues could be explained by changes in element concentrations in the soils and by direct element uptake from the air, as well as by the antagonistic relationships between the elements.     

comparison of sulphur and heavy metal contents and their regional distribution in humus and moss samples from the vicinity of Nikel and Zapoljarnij,Kola Peninsula,Russia

Terrestrial moss and humus (the O-horizon) are often used separately for determining and monitoring airborne heavy metal pollution. Here, we directly compare the results of analyses of moss and humus samples taken at a density of one site per 300 km² in a 12 000 km² area (45 samples) around the nickel smelter in Nikel, the nickel ore roasting plant in Zapoljarnij, both in Russia, and the iron ore mine and mill near Kirkenes in Norway. The samples were air dried, digested in conc. HNO₃ and analysed for more than 30 elements by ICP-MS and ICP-AES at the laboratory of the Geological Survey of Finland (GTK). For most elements, observed levels and variations are considerably greater in soil than in moss. The main contaminants, Ni and Cu, reach equally high median levels in the moss and soil, but maximum values are far higher in soil. Both media show comparable regional distribution patterns for the heavy metals, but not for sulphur. Cu and Ni can be used to delineate the limits of contamination in the survey area. Both media show the same picture, with a generally very steep gradient from east to west and background levels being reached 30–50 km from the nickel smelter. When moss is used, Cu/Ni, Cu/S and Ni/S ratios can be used to separate input from the smelting and roasting proccesses in Russia. Both media are well suited to use separately to detect airborne pollution in this heavily contaminated area. The moss data are generally easier to interpret, but moss is not available at the most polluted sites. Levels for many elements other than Cu and Ni are close to the detection levels in moss samples, but not in humus samples. Information gathered from both media thus complement each other in a regional multi-element survey.     

Evaluation of regional heavy metal deposition by multivariate analysis of element contents in pine tree barks

The airborne immission of heavy metals in the conservation area “Dübener Heide” nearby Bitterfeld was evaluated by biomonitoring studies with bark samples of 60-years-old scots pine (Pinus sylvestris L.). Nitric acid digestion and hydrochloric acid extraction of bark was followed by ICP-AES and ICP-MS analysis of the elements Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn. Fe and especially Cr were only partly soluble in hydrochloric acid. These elements deposited mostly as insoluble oxides, and their contents in the bark correlate significantly with Ca and S as elements of alkaline and acid deposition. Factor and cluster analysis of all element contents are used for the characterization and evaluation of heavy metal deposition types, which is shown to be a useful tool in forest monitoring control.     

Determination of “normal” levels and upper limit values of trace elements in soils

To determine “normal” levels of trace elements in soils, soil samples taken all over Belgium were analysed. The selection of the sampling places was based on the geological substrata, from which the soils originate and on the texture class to which they belong. The elements As, B, Be, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sb, Se, Ti, V and Zn were determined using an extraction method with strong acids. The found concentrations were called “total acid extraction concentrations”, although this extraction does not extract all the elements which are incorporated into the minerals. This has been done, however, by arc emission spectrography which was applied to determine the elements Ag, B, Co, Cr, Ga, Mo, Ni, Sn, Sr and V. The greatest difference between the “overall total” concentrations and the “total extractable concentrations” were found for chromium. Based on the obtained results, an upper limit for normal levels of trace elements was fixed. For Ag, Cd, Hg, Pb and Sb, this upper limit value is almost the same for all the investigated soils irrelevant of their texture. The same conclusion could not be made for the other elements. For these elements, the soil texture and also the geological parent material, on which the soil was formed, have an influence on the upper limit value.     

Arsenic and Heavy Metal Uptake and Accumulation in Native Plant Species from Soils Polluted by Mining Activities

Arsenic and heavy metal (specifically Cd, Cr, Cu, Ni, Pb, and Zn) uptake, translocation, and accumulation in ten native plant species spontaneously growing in soils polluted by mining activities were studied, with a focus on future phytoremediation work in polluted soils. Plant and soil samples were collected in the vicinity of the Mónica mine (NW Madrid, Spain). Soil analysis showed the ability of native plants for growing in soils with high concentration levels of Cd, Cu, Pb, Zn, and especially As. From these elements, the highest percentage of extractable elements was found for Cd and the lowest for Pb. A highly significant correlation was observed between total and extractable element concentrations in soils, except for Cu, indicating that total concentration is the most relevant factor for element mobility in these soils. Extractable elements in soils were better correlated with concentrations in plants than total elements in soils; thus, extraction methods applied are suitable to estimate the element phytoavailable fraction in soils, which depends on the plant species and not only on the element mobility in soils. High element concentrations were found in the aboveground parts of Corrigiola telephiifolia (As and Pb), Jasione montana (Cd and Zn), and Digitalis thapsi (As, Cd, Cu, Pb and Zn). However, considering the translocation and accumulation factors, together with the concentration levels found in roots and aboveground parts, only C. telephiifolia could be considered a Pb accumulator and an As hyperaccumulator plant, which could be used for future phytoremediation work in soils polluted with As.     

Heavy metal deposition in Scandinavia

Maps showing the regional differences in the atmospheric deposition of Pb, Cd, Hg, Cr, Ni, Cu, Zn, and Fe have been prepared for Finland, Norway and Sweden from data obtained by means of moss analysis, a method previously shown to be a sensitive and reliable tool in measuring heavy metal deposition. In all elements the minima were recorded in northern Norway, the maxima in south-central or south-western Sweden and southernmost Norway. The greatest regional differences were measured in Pb and Cd.     

Evaluation and source identification of trace element contamination of soils in the Qixia lead-zinc mining area,Jiangsu, China

Purpose

The Qixia mine is one of the largest lead-zinc mines in Eastern China and has been operational for approximately 60 years. Source identification for trace element contamination of soils in the Qixia mining area has been lacking. This report details the evaluation and source identification of trace element contamination (including Cu, Zn, Pb, Cd, Hg, Cr, As, and Ni) of soils in this area.

Materials and methods

Thirty-three soil samples from roadsides and fields in the study area were collected and analyzed. The index of geo-accumulation (I _geo) was employed to evaluate contamination. Methods of multivariate statistical analysis were used to determine the probable sources of the pollutants.

Results and discussion

The analysis showed that the levels of contamination ranked in the following order: Cd > Pb/Zn> > As/Cu> > Hg > Cr/Ni. In the sampling area nearest the mine, soil samples collected from roadsides showed much higher levels of contamination than those collected from fields away from the roadways. Trace element contamination decreased as the distance from the mine increased. Contamination extended to a distance of approximately 700 m from mineral transportation routes, with the area of greatest impact at 200 m or less. Multivariate statistical analysis and ore composition data suggest that the Cu, Zn, Pb, Cd, and As found in the soil samples originate from anthropogenic sources. Ni and Cr are considered to be at natural background concentrations.

Conclusions

This study distinguished between natural and anthropogenic sources of trace element contamination in the soils of the Qixia mining area. The contamination of Cu, Zn, Pb, Cd, and As is linked to the mining activities and is likely due to the transportation of ore concentrates and tailings.     

Anthropogenic environmental impact in the Mediterranean coastal area of Koper/Capodistria,Slovenia

Purpose

Heavy metal content in soils could be a consequence of geogenic and different anthropogenic sources. In ancient times, soils in the Mediterranean region were affected by agriculture and viticulture, whereas more recently, industry and traffic might contribute more to their pollution. The aim of the study is to determine the extent of multisource heavy metal pollution in soils within the Koper area.

Materials and methods

Along the northern Adriatic Sea coast, around the port city of Koper/Capodistria, 24 topsoil samples were collected; sets of six samples representing four possible pollution sources: intensive agriculture, viticulture, port activities and industry. The parent material of the soil is mainly derived from the Eocene flysch weathered marls and calcarenites and the soil types are eutric. The chemical composition of the samples was determined by ICP-ES for oxides and several minor elements and by ICP-MS for heavy metals. The mineral composition of the selected samples was checked using X-ray powder diffraction. Different statistical analyses were performed on the normally distributed data.

Results and discussion

The mean concentrations of all samples are: Cr 215 mg kg^?1, Ni 81 mg kg^?1, Zn 67 mg kg^?1, Cu 44 mg kg^?1 and Pb and Co 18 mg kg^?1. The ANOVA showed significant differences only in CaO, C/TOT, P₂O₅, Co and Pb between those locations within reach of the different contamination sources. The observed average values of heavy metals are well below Slovenia’s Directive limit for Cu, Pb and Zn, close to but not above it for Co and above the action value for Cr and Ni. According to Igeo, soils from all the sampling locations are uncontaminated with Co, Ni and Pb, and uncontaminated to moderately contaminated with Cu and Zn at one port location, and with Cr at all locations.

Conclusions

The very high Cr and Ni levels could still be geogenic because soils developed on Eocene flysch rocks are enriched in both metals. Cr and Ni are not correlated because of their different levels of sorption and retention in carbonate soils. Cr was retained and concentrated in the sand fraction but Ni has been mobilised in solution. The only serious threat to the environment seems to be an illegal waste dumping area near the port.     

Trace Element Analysis via Open‐Vessel or Microwave‐Assisted Digestion in Calcareous Mediterranean Soils

Abstract

Different digestion methods can be applied for analyzing trace elements in soils. Selection of the most useful and convenient method is critical for the adequate determination of their concentrations in each type of soil to appropriately detect potential environmental pollution. Open‐vessel digestion using a digester block (method 1) and microwave‐assisted digestion (method 2) were compared using a certified reference material (CRM) with similar properties and characteristics to calcareous Mediterranean soils. Both methods were contrasted in terms of accuracy by calculating the recovery of cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) in the CRM and precision of replicate analysis through the relative standard deviation (RSD). Recoveries from the digester block method were slightly higher than recoveries from microwave digestion because the use of perchloric acid (HClO₄), whereas RSD values for microwave digestion were generally lower but with higher measured precision than values obtained by open‐vessel digestion. The digestion methods were compared for analyzing trace elements in calcareous agricultural soils devoted to vegetable crops in the Alicante province (southeast Spain), as a representative area of the European Mediterranean region. Results of the paired‐sample t‐test showed significant differences between both methods for Co, Cr, Cu, and Pb in calcareous Mediterranean soils, whereas regression analysis indicated a good correlation between both methods for Cu, Ni, Pb, and Zn. Consequently, the choice of the digestion method is more relevant for minor elements such as Co and Cr. Microwave‐assisted digestion seems to be the best option to determine most of the trace elements in calcareous Mediterranean soils, because closed‐vessel digestion exhibited lower variability according to the RSD values obtained in the study area, particularly for Co and Cr. Trace element concentrations were in agreement with background levels, except for Cu and Pb in some soils, which seem to be related to anthropic activities.     

Geochemical behaviour of Ni,Cr, Cu,Zn and Pb in an Andosol–Cambisol climosequence on basaltic rocks in the French Massif Central

The objective of this study is to identify parameters influencing trace elements (TE) vertical distributions in an Andosol–Andic Cambisol climosequence. In order to understand processes involved in the current distribution of trace elements from basaltic rocks to associated soils, six pedons developed on Tertiary massive basaltic formations, located at similar position in the hill-slopes, submitted to the same wet mountainous climate but under various microclimatic conditions (altitude and annual rainfall), were considered. The six studied soils are andic and rich in organo–metallic complexes. Two different and quantitative methods were used to compare the geochemical distributions of major and trace elements, both being calculated with Ti as invariant element: isovolumetric mass balance and enrichment factors. Anthropogenic, pedogenetic, microclimatic, inherited factors were discriminated. Anthropogenic influences are pointed out for K in two pedons and for Pb in all studied sites. Distributions of other TE are affected by discontinuities between underlying rocks and soil horizons. Zinc and Cu distributions are controlled by organic matter whereas Cr and Ni distributions are influenced by pedogenetic processes. Results emphasize the relative trace element immobilization in andic soils under temperate climate.     

Trace element concentrations and background values in the arid soils of Hormozgan Province of southern Iran

Trace element concentrations in soils of arid regions of southern Iran are described to assess the concentration ranges of selected elements in a variety of soils and rocks, and to evaluate the potential bioavailability of trace elements in relation to soil properties. The study area was classified into three sub-regions consisting of (1) shale, gypsum, and limestone (western part), (2) igneous rocks and limestone (northern part), and (3) sandstone and limestone (eastern and northeastern part). The gained background values of trace elements were used for evaluating the quality and degree of contamination with native and also with anthropogenic elements of studied soils. Some soil samples indicated a significant enrichment for Pb and Ni, with an enrichment factor (EF) of around 6.0. Soils have only been cultivated for few years compared to hundreds and thousands of years for many agricultural soils; therefore, there has been less crop removal. Furthermore, soils are not highly weathered because they are in an arid climate with low precipitation, which results in a slow rate of weathering. However, slight elemental differences between soil horizons indicated that most soils are poorly developed and also represented the similarity of trace element contents between soils and parent materials.     

Distribution of Lead,Cobalt and Nickel in the Soil Around a Coal-Fired Power Plant

To determine the effect on the environment of heavy metal emissions from power plants, the contents of Pb, Co and Ni in the soils around a medium sized, hard-coal-fired power plant were measured. In the fly ash from the last state of the electrostatic precipitator these elements were present in the following concentrations: Pb: 3680; Co: 122 and Ni: 325 mg/kg. The metal contents in the soil around the plant (0.4–5.2km) were in the same range as observed with other soils in Germany (Pb: 15–35; Co: 4–16; Ni: 5–40 mg/kg). Due to the fact that in this area the frequency of westerly winds is considerably higher than that of southerly winds, increased concentrations of these metals in samples east of the plant may be expected compared to those collected north of it. The distribution of the metal contens in the soil around the plant does not, however, suggest such an effect. The airborne emissions of Pb, Co and Ni near the plant are obviously too small to change significantly the local distribution pattern of these elements in the soil.     

Transmission of Atmospherically Derived Trace Elements Through an Undeveloped, Forested Maryland Watershed

The transmission of atmospherically derived trace elements (Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Se, and Zn) was evaluated in a small, undeveloped, forested watershed located in north-central Maryland. Atmospheric input was determined for wet-only and vegetative throughfall components. Annual throughfall fluxes were significantly enriched over incident precipitation for most elements, although some elements exhibited evidence of canopy release (Mn) or preferential uptake (As, Cr, and Se). Stream export was gauged based on systematic sampling under varied flow regimes. Particle loading appears to contribute significantly to watershed export (> 10%) for only As, Pb, and Fe, and then only during large precipitation/runoff events. The degree of watershed transmission for each trace element was evaluated based on a comparison of total, net atmospheric input (throughfall) to stream export over an annual hydrologic cycle. This comparison indicates that the atmospheric input of some elements (Al, Cd, Ni, Zn) is effectively transmitted through the watershed, but other elements (Pb, As, Se, Fe, Cr, Cu) appear to be strongly sequestered, in the respective orders noted. Results suggest that precipitation and subsequent soil pH are the primary factors that determine the mobility of sequestered trace element phases. To further resolve primary atmospheric and secondary weathering components, the geochemical model NETPATH was applied. Results indicate that minerals dissolved include chlorite, plagioclase feldspar, epidote, and potassium feldspar; phases formed were kaolinite, pyrite, and silica. The model also indicates that weathering processes contribute negligible amounts of trace elements to stream export, indicative of the unreactive orthoquartzite bedrock lithology underlying the watershed. Thus, the stream export of trace elements primarily reflects atmospheric deposition to the local watershed.     

Atmospheric deposition of trace elements in Norway: Temporal and spatial trends studied by moss analysis

The atmospheric deposition of sixteen trace elements, as inferred by their concentration in moss samples collected in 1985 from 500 sites in Norway, is compared with data from a similar survey in 1977. The deposition patterns of V, Zn, As, Se, Cd, Sb, and Pb are substantially influenced by long-range transport from other parts of Europe, but a general decline is evident from 1977 to 1985, most strongly for Pb. For Cr, Fe, Co, Ni, and Cu the deposition patterns are largely determined by contributions from point sources within Norway and on the Kola peninsula close to the Russian/ Norwegian border. The moss data for Br, I, and partly Se reflect airborne supply from the marine environment, whereas Al and Sc serve as indicators of contributions from soil dust. Contributions to the trace element concentrations in moss from sources other than atmospheric deposition are identified and discussed.     

Spatial Heterogeneity in the Properties of High-Moor Peat Soils under Local Pyrogenesis in Northeastern Sakhalin

The structure and properties of oligotrophic peat, oligotrophic peat gley, and pyrogenic oligotrophic peat soils identified on a plot 0.5 km² in area in the northeast of Sakhalin Island have been studied. The vertical distributions of physicochemical, chemical, and ecotoxicological parameters in the profiles of some bog soil groups have been considered. An increase in ash content, a less acid reaction, and a deficit of available nitrogen and potassium have been revealed in the upper horizons of pyrogenic soils. No accumulation of mobile heavy metals is manifested in the pyrogenic horizons of peat soils. Statistical parameters of the spatial variation in pH_KCl and total acidity, as well as the contents of ash, available phosphorus, exchangeable potassium, ammonium and nitrate nitrogen, mobile heavy metals (Cr, Ni, Cu, Zn, Cd, Pb), and benzo[a]pyrene, have been calculated for the moss and sublitter horizons. The variation coefficients are 30–100% for most of the studied parameters and reach 100–200% for available phosphorus; ammonium nitrogen; and mobile Ni, Cu, Zn, and Cd. An increase in the content of benzo[a]pyrene, although without MPC exceedance, is noted in the moss of pyrogenic soils and the peat horizons untouched by fires.     

Determining baseline element composition of lichens

Element-concentration baselines are given for Parmelia sulcata and associated soils. Parmelia chlorochroa was found sporadically and therefore only representative concentration ranges are reported for this species. Element data include (1) for lichens; Al, As, Ba, B, Ca, Cr, Cu, Fe, Hg, Mn, Ni, P, Sr, S, Ti, V, Y, and Zn; and (2) for soils: Al, Ba, Be, Ca, Cs, Cr, Cu, Fe, Hg, Mg, Mn, Ni, Nb, P, Pb, Sr, S, Ti, V, Y, and Zn. Very little (usually < 10 %) of the variability in the element data for lichen material occurs regionally (> 7.2 km); thus, P sukata is, in general, chemically similar throughout the park. This same uniformity was found for soil geochemistry. Numerous samples collected at close intervals would be required, therefore, to produce detailed element-concentration maps for P. sulcata and soils. No instances of elemental phytotoxic conditions were found; however, P. sulcata apparently possesses large concentrations of Ba, Cu, Fe, Pb, S, V, and possibly Zn.     

Trace Elements In Water,Fish and Sediment from Tuskegee Lake,Southeastern Usa

The concentrations of trace elements in water, sediment and fish samples from Tuskegee Lake located in Southeastern United States were investigated in this study. The Lake is utilized both as a source for municipal drinking water, and for recreational fishing. The water quality characteristics over two sampling periods, the speciation of metals in the Lake sediments, the risk to water column contamination and levels of heavy metals in largemouth bass (Micropterus salmoides) samples from the Lake were evaluated. The Lake water quality characteristics were mostly below the recommended drinking water standards by the United StatesEnvironmental Protection Agency (US EPA) and the European Union (EU) except for aluminum, iron, manganese and thallium. In addition, the average values of Cr, As, Mn, Zn and Cl^- in the water samples analyzed were higher than the respective reference values for fresh water. To study the speciation of metals in the Lake sediments, ten elements (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V, and Zn) in four grain sizes (< 710 μm – 250 μm, < 250 μm – 75 μm, < 75 μm – 53μm, and < 53 μm) were subjected to sequential extractions. Irrespective of grain size, the elements analyzed were distributed in both the non-residual and residual phases except Ni that was found only in the residual fraction. The potential risk to Lake water contamination was highest downstream (Sites 1 and 2) based on the calculated global contamination factors. From the calculated individual contamination factors, Mn and Pb followed by Zn, Cu, Cr, Co and V posed the highest risk to water contamination. Based on this study, the human health risks for heavy metals in fish caught from Tuskegee Lake are low for now, and irrespective of the source of fish, concentrations of metals in muscle tissues were all below the recommended Food and Agriculture Organization (FAO) maximum limits for Pb (0.5 mg Kg^-1), Cd (0.5 mg Kg^-1), Cu (30 mg Kg^-1), and Zn (30 mg Kg^-1) in fish.