Grain size partitioning of platinum-group elements in road-deposited sediments: implications for anthropogenic flux estimates from autocatalysts

Twelve road-deposited sediment samples were analyzed for platinum-group elements (PGEs) and Pb in the <63 microm fraction of an urban watershed in Hawaii. Three samples were further fractionated into five size classes, from 63-125 microm to 1000-2000 microm, and these were analyzed for PGEs and Pb. Concentrations in the <63 microm fraction reached 174 microg/kg (Pt), 101 microg/kg (Pd), 16 microg/kg (Rh), and 1.3 microg/kg (Ir). Enrichment ratios followed the sequence Rh>Pt=Pd>Ir. Iridium was geogenic in origin, while the remaining PGEs indicated significant anthropogenic contamination. Palladium, Pt and Rh concentrations and enrichment signals were consistent with PGE bivariate ratios and PGE partitioning in three-way catalysts. Size partitioning indicated that the <63 microm fraction had the lowest PGE concentrations and mass loading percentages. These data suggest that autocatalyst PGE flux estimates into the environment will be significantly underestimated if only a fine grain size fraction is analyzed.     

Multi-element analysis of road-deposited sediment in an urban drainage basin, Honolulu, Hawaii

Road-deposited sediment (RDS) and its associated contaminant load play a critical role in degrading receiving water bodies. Few quantitative multi-element RDS studies exist, and there are none from Hawaii. This lack of baseline data combined with concerns with high concentrations of Pb and Cu in fish and enrichment of Cu, Pb and Zn in bed sediments from Manoa Stream, Hawaii, lead to a detailed characterization of RDSs in Manoa basin. Data for a total analysis of 23 elements using inductively coupled plasma atomic-emission spectrometry and instrumental neutron activation analysis and 16 elements using a 0.5 M HCl partial leach are presented for RDSs and background soils. Concentration data, comparisons with environmental guidelines, and concentration enrichment ratios (CERs) all indicate that RDS in Manoa has a significant degree of anthropogenic pollution. The most environmentally important elements were Pb, Sb and Zn. Concentrations of these elements, primarily vehicle contributed, compare favorably with those from other studies of RDS. The high mean concentration of Pb (151 mg/kg) compared to background soils (13 mg/kg) indicates remobilization of Pb previously stored in soils and transported to road surfaces by water erosion processes. The higher Pb CER(Total) in RDSs compared to bed sediments from Manoa Stream suggests a potential link via ubiquitous storm drains and subsequent dilution with less contaminated fluvial sediments. Data from the HCl leach also support Pb and Zn as having significant anthropogenic signals, and Cu having a moderate signal. These data indicate that RDSs in Manoa basin are generally contaminated with certain potentially toxic elements and the legacy of past use of leaded gasoline is still a concern in this urban drainage system.     

Distribution of lead, copper and zinc in size-fractionated river bed sediment in two agricultural catchments of southern Ontario, Canada

Metal (Pb, Cu and Zn) partitioning in six separated sediment size fractions (<8, 8-12, 12-19, 19-31, 31-42, 42-60 microm) of river bed sediment have been analyzed by sequential extraction. The concentrations of some major elements (Si, Al, Ca, Mg, K, Na, Fe, Mn and P), and organic and inorganic C were determined to correlate the elemental composition of the sediment with metal speciation and grain size. Results show that Zn and Pb concentrations increase with decreasing grain size. For Big Creek and Big Otter Creek, respectively, the highest concentrations of Zn (326 and 230 mg kg(-1)) and Pb (158 and 67 mg kg(-1)) were found in the smallest (<8 microm) fraction, whereas the Cu levels (619 and 1281 mg kg(-1)) were most abundant in the second smallest (8-12 microm) fraction. The major accumulative phases for Cu, Zn and Pb were carbonates, Fe/Mn oxides and organic matter, but the relative importance of each phase varied for individual metals and grain sizes. The extraction data show increasing potential bioavailability of metals with decreasing grain size. Estimates of metal yields in the study catchments suggest that over 80% of the metal yield in sediment smaller than 63 microm is associated with solids smaller than 31 microm.     

Toxicity and heavy metal contamination of surficial sediments from the Bay of Thessaloniki (Northwestern Aegean Sea) Greece

Surficial sediments (the fraction < 2000 microm) from the Bay of Thessaloniki, in the Northwestern Aegean Sea, Greece were examined for heavy metal and organic carbon contents, as well as for acute LUMIStox toxicity of pore waters (PWs), wet sediment elutriates (WSEs) and dry sediment elutriates (DSEs) obtained from the solid material remaining after PW extraction. WSEs where not toxic. EC20/50 values could be measured in some DSE and PW samples. In all sediment samples, the DSE toxicity was greater than the corresponding PW toxicity. Sediment concentrations of total and labile Cd, Pb, Cu, Cr, Zn, Mn, Ni and Fe were determined and evaluated in relation to sediment quality guidelines. Pollution levels ranged from low to high for certain metals. A misfit between sediment toxicities calculated from heavy metal concentrations and those biologically measured was observed. Toxicity values were in general poorly correlated with sediment's heavy metal or organic carbon content. As significant correlation was however found between the DSE toxicity with total Ni and labile Fe, as well as for the PW toxicity with total Ni, labile Fe and labile Cr.     

Labile and non-labile desorption rate constants for 33 PCB congeners from lake sediment suspensions

Lake sediments contaminated with polychlorinated biphenyls (PCBs) were purged using a gas stripping technique to estimate desorption rate constants. Desorption profiles and modeling of the data clearly show a two-step release of PCBs from sediment suspensions that can be described as a labile (fast) release followed by a non-labile (slow) release. Data are summarized by labile and non-labile rate constants and by mass in each phase as a function of suspended solids concentration for twelve pure congeners and nine co-eluting data sets (twenty-one chromatograph peaks total). Labile desorption rate constants range from 113 days(-1) to 1.43 days(-1) for the 100 mg/l sediment suspension, from 67.7 days(-1) to 2.45 days(-1) for the 1000 mg/l sediment suspension, and from 8.41 days(-1) to 0.946 days(-1) for the 5000 mg/l sediment suspension. Labile rate constants consistently decreased with increasing suspended solids, and, in general, decreased with increasing degree of chlorination (reflected in increasing retention time in the chromatogram). No consistent trend was observed for the non-labile rate constants with suspended solids concentration or degree of chlorination. The average non-labile rate constant for the PCB congeners studied here was 0.154 days(-1) (s.d.=0.158; n=63). The distribution between the labile and non-labile phases also failed to indicate dependence on suspended solids concentration, chlorine substitution pattern, or molecular weight of the congener, although the data from the 5000 mg/l suspension consistently contained less labile components. The average distributions (n=63) were 60.1% in the labile phase and 39.9% in the non-labile phase.     

Heavy metal distribution in marine sediments from the southwest coast of Spain

The latest version (1999) of the BCR-sequential extraction technique was used to determine the distribution of metals (Cu, Zn, Cd, Pb, Fe, Ni, Cr, and Mn) with major sedimentary phases (acid-soluble, reducible, oxidisable and residual) in samples from the southwest coast of Spain. The total metal content was also determined. The results showed that an extensive area along the coast (35 km long), near the joint mouth of the Tinto and Odiel Rivers, contains sediments with high concentrations of metals, with maximums of 649 mg/kg of Zn, 336 mg/kg of Cu, 197 mg/kg of Pb and 2.5 mg/kg of Cd. The values found for Cr, Ni and Mn are comparable to those in unpolluted areas. Based on the chemical distribution of metals, we found that Zn is the most mobile (i.e., it can pass easily into the water under changing environmental conditions). This metal showed the highest percentages in the acid-soluble fraction (the most labile), especially in the central coastal area, where the samples contained over 50% of this element associated with this fraction. This area close to the Tinto and Odiel river mouths also shows a significant increase in the mobility of Cd and Cu. In both cases the amount present in the residual fraction is lower, and the acid-soluble fraction is increased for Cd and the oxidisable fraction for Cu. However, the highest percentages of Fe, Cr and Ni are found in the residual fraction (84%, 89% and 75%, respectively), which implies that these metals are strongly bound to the sediments.     

Arsenic Background Definition: Introduction and Objectives

Produced water samples from the Bacia de Campos oil field offshore Pargo and Pampo platforms were analyzed for Ba, 226 Ra, 228 Ra, V, Ni and Pb. The activity concentrations measured were in the range of 1.6-6.0 Bq/L for 226 Ra and 0.7-8.2 Bq/L for 228 Ra for both platforms. For Ba, V, Ni and Pb the concentrations measured were in the range of 5.6-25.7 mg/L, 0.15-0.46 µg/L, 4.85-12.14 µg/L and 4.04-12.37 µg/L. A strong correlation between barium and radium isotopes concentration was observed ( 226 Ra: R 2 = 0.897; 228 Ra: R 2 = 0.737). In order to evaluate the environmental impact from discharges of produced water into the sea, the seawater and sediment samples were collected at distances from 250 to 1000 m around the platforms. The seawater samples were analyzed for dissolved and particulate material and the sediment samples for total and leachable fraction. The results show that even for the shortest sampling distance (250 m) from the discharge point, Ba, 226 Ra, 228 Ra, V, Ni and Pb concentrations in seawater and sediment were similar to the local background, indicating that dispersion by local currents minimizes any environmental impact involving these parameters.     

A simple and fast screening test to detect soils polluted by lead

Lead pollution is an environmental priority. The evaluation of contaminated soils was often based on the results of the toxicity characteristic leaching procedure (TCLP) or the synthetic precipitation leaching procedure (SPLP). This paper presents a simple and fast screening test to detect soil contaminated by lead. The test is based on the chemistry of the stomach (Cl- concentration, pH 2, T = 37 degrees C) and simulates the incidental oral ingestion of soil by young children. The gastric juice simulation test (GJST) and the TCLP were applied to six size fractions from five soils. The GJST solubilized more Pb (up to 169 mg/l) than the TCLP especially for the smallest size fraction. Particle size had less effect on the TCLP. The percentage of lead released with the GJST, was most significant for the <63 microm size fraction and varied from 18 to 74% of the total lead content. Lead leached during the TCLP as a function of the total lead content showed poor linear regression coefficient (R) values for soils <250 microm. R values were significant for all size fractions with the GJST. The pH of approximately 5 in the TCLP limits the solubilization of lead in the small size fractions. The five soils exceeded the toxicity threshold of 10 microgPb/dl of blood for a significant fraction of children between 0 and 36 months using the EPA's IEUBK model (Integrated Exposure Uptake Biokinetic). But the TCLP did not detect lead contamination in two of these five soils. The GJST proved to be a better estimator of lead bioaccessibility in the gastrointestinal tract.     

Factors affecting the concentrations of lead in British wheat and barley grain

The entry of Pb into the food chain is of concern as it can cause chronic health problems. The concentration of Pb was determined in cereal grain samples collected representatively from British Cereal Quality Surveys in 1982 and 1998 (n = 176, 250 and 233 for wheat collected in 1982 and 1998, and barley in 1998, respectively). In addition, paired soil and grain samples were collected from 377 sites harvested across Britain in 1998-2000. Wheat grain Pb ranged from below the analytical detection limit (0.02 mg kg(-1) dry weight, DW) to 1.63 mg kg(-1) DW, and barley grain Pb from <0.02 to 0.48 mg kg(-1) DW. The vast majority of samples (>99% for both wheat and barley, excluding Scottish barley samples collected in 2000) were well below the newly introduced EU limit for the maximum permissible concentration of Pb in cereals (0.2 mg kg(-1) fresh weight, equivalent to 0.235 mg kg(-1) DW). There was a significant reduction in wheat grain Pb in the 1998 survey compared with the 1982 survey. However, 40 barley samples collected from Scotland in 2000 in the paired soil and crop survey showed anomalously high concentrations of Pb, with 10 samples exceeding the EU limit. Washing experiments demonstrated that surface contamination, introduced during grain harvest and/or storage, was the main reason for the high concentrations in these samples. In the paired soil and crop surveys, there were no significant correlations between grain Pb concentrations with total soil Pb and other soil properties, indicating low bioavailability of Pb in the soils and limited uptake and transport of Pb to grain. The Pb in cereal grain is likely to originate mainly from atmospheric deposition and other routes of surface contamination during harvest and storage.     

Contents and leachability of heavy metals (Pb, Cu, Sb, Zn, As) in soil at the Pantex firing range, Amarillo, Texas.

Pantex firing range soil samples were analyzed for Pb, Cu, Sb, Zn, and As. One hundred ninety-seven samples were collected from the firing range and vicinity area. There was a lack of knowledge about the distribution of Pb in the firing range, so a random sampling with proportional allocation was chosen. Concentration levels of Pb and Cu in the firing range were found to be in the range of 11-4675 and 13-359 mg/kg, respectively. Concentration levels of Sb were found to be in the range of 1-517 mg/kg. However, the Zn and As concentration levels were close to average soil background levels. The Sn concentration level was expected to be higher in the Pantex firing range soil samples. However, it was found to be below the neutron activation analysis (NAA) detection limit of 75 mg/kg. Enrichment factor analysis showed that Pb and Sb were highly enriched in the firing range with average magnitudes of 55 and 90, respectively. Cu was enriched approximately 6 times more than the usual soil concentration levels. Toxicity characteristic leaching procedure (TCLP) was carried out on size-fractionated homogeneous soil samples. The concentration levels of Pb in leachates were found to be approximately 12 times higher than the U.S. Environmental Protection Agency (EPA) regulatory concentration level of 5 mg/L. Sequential extraction (SE) was also performed to characterize Pb and other trace elements into five different fractions. The highest Pb fraction was found with organic matter in the soil.     

Effect of weathering product assemblages on Pb bioaccessibility in mine waste: implications for risk management

General assessments of orebody types and associated mine wastes with regard to their environmental signature and human health hazards are needed to help in managing present and historical mine waste facilities. Bioaccessibility tests and mineralogical analysis were carried out on mine waste from a systematic sampling of mine sites from the Central Wales orefield, UK. The bioaccessible Pb widely ranged from 270 to 20,300 mg/kg (mean 7,250 mg/kg, median 4,890 mg/kg), and the bioaccessible fraction from 4.53 to >100 % (mean 33.2 %, median 32.2 %), with significant (p?=?0.001) differences among the mine sites. This implies sensitivity of bioaccessibility to site-specific conditions and suggests caution in the use of models to assess human health impacts generalised on the basis of the mineral deposit type. Mineralogical similarities of the oxidation products of primary galena provided a better control over the observed Pb bioaccessibility range. The higher Pb bioaccessibility (%) was related to samples containing cerussite, irrespective of the presence of other Pb minerals in the mineral assemblage; lower Pb bioaccessibility resulted where anglesite was the main Pb mineral phase and cerussite was absent. A solubility diagram for the various Pb minerals in the waste was derived using PHREEQC model, and the experimental Pb concentrations, measured in the simulated gastric solution, were compared with the equilibrium modelling results. For samples containing cerussite, the model well predicted the soluble Pb concentrations measured in the gastric solution, indicative of the carbonate mineral phase control on the Pb in solution for these samples and little kinetic control on the dissolution of cerussite. On the contrary, most mine waste samples containing dominant anglesite and or plumbojarosite (no cerussite) had lower solution Pb values, falling at or below the anglesite and plumbojarosite solubility equilibrium concentrations, implying kinetic or textural factors hindering the dissolution.     

Environmental Impact in Sediments and Seawater due to Discharges of Ba, 226Ra, 228Ra,V, Ni and Pb by Produced Water from the Bacia de Campos Oil Field Offshore Platforms

Produced water samples from the Bacia de Campos oil field offshore Pargo andPampo platforms were analyzed for Ba, ²²⁶Ra, ²²⁸Ra, V, Ni and Pb. The activity concentrations measured were in the range of 1.6–6.0 Bq/L for ²²⁶Ra and 0.7–8.2 Bq/L for ²²⁸Ra for both platforms. For Ba, V, Ni and Pb the concentrations measured were in the range of 5.6–25.7 mg/L, 0.15–0.46 μg/L, 4.85–12.14 μg/L and 4.04–12.37 μg/L. A strong correlation between barium and radium isotopes concentration was observed (²²⁶Ra: R² = 0.897;²²⁸ Ra: R² = 0.737). In order to evaluate the environmental impact from discharges of produced water into the sea, the seawater and sediment samples were collected at distances from 250 to 1000 m around the platforms. The seawater samples were analyzed for dissolved and particulate material and the sediment samples for total and leachable fraction. The results show that even for the shortest sampling distance (250 m) from the discharge point, Ba, ²²⁶Ra, ²²⁸Ra, V, Ni and Pb concentrations in seawater and sediment were similar to the local background, indicating that dispersion by local currents minimizes any environmental impact involving these parameters.     

Lead pollution in a large, prairie-pothole lake (Rush Lake, WI, USA): effects on abundance and community structure of indigenous sediment bacteria

Rush Lake (WI, USA), the largest prairie-pothole lake east of the Mississippi River, has been contaminated with lead pollution as a result of over 140 years of waterfowl hunting. We examined: (1) the extent of lead pollution in Rush Lake sediments and (2) whether lead pollution in Rush Lake is affecting the abundance and community structure of indigenous sediment bacteria. Sediment lead concentrations did not exceed 59 mg Pb kg(-1) dry sediment. No relationship was observed between sediment lead concentration and the abundance of aerobic (P=0.498) or anaerobic (P=0.416) heterotrophic bacteria. Similarly, lead did not appear to affect bacterial community structure when considering both culturable and nonculturable community members. In contrast, the culturable fraction of sediment bacteria in samples containing 59 mg Pb kg(-1) exhibited a unique community structure. While factors other than lead content likely play roles in determining bacterial community structure in the sediments of Rush Lake, these data suggest that the culturable fraction of sediment bacterial communities is affected by elevated lead levels.     

The EDTA effect on phytoextraction of single and combined metals-contaminated soils using rainbow pink (Dianthus chinensis)

Rainbow pink (Dianthus chinensis), a potential phytoextraction plant, can accumulate high concentrations of Cd from metal-contaminated soils. The soils used in this study were artificially added with different metals including (1) CK: original soil, (2) Cd-treated soil: 10 mg Cd kg(-1), (3) Zn-treated soil: 100 mg Zn kg(-1), (4) Pb-treated soil: 1000 mg Pb kg(-1), (5) Cd-Zn-treated soil: 10 mg Cd kg(-1) and 100 mg Zn kg(-1), (6) Cd-Pb-treated soil: 10 mg Cd kg(-1) and 1000 mg Pb kg(-1), (7) Zn-Pb-treated soil: 100 mg Zn kg(-1) and 1000 mg Pb kg(-1), and (8) Cd-Zn-Pb-treated soil: 10 mg Cd kg(-1), 100 mg Zn kg(-1), and 1000 mg Pb kg(-1). Three concentrations of 2Na-EDTA solutions (0 (control), 2, and 5 mmol kg(-1) soil) were added to the different metals-treated soils to study the influence of applied EDTA on single and combined metals-contaminated soils phytoextraction using rainbow pink. The results showed that the Cd, Zn, Pb, Fe, or Mn concentrations in different metals-treated soil solutions significantly increased after applying 5 mmol EDTA kg(-1) (p<0.05). The metal concentrations in different metals-treated soils extracted by deionized water also significantly increased after applying 5 mmol EDTA kg(-1) (p<0.05). Because of the high extraction capacity of both 0.005 M DTPA (pH 5.3) and 0.05 M EDTA (pH 7.0), applying EDTA did not significantly increase the Cd, Zn, or Pb concentration in both extracts for most of the treatments. Applying EDTA solutions can significantly increase the Cd and Pb concentrations in the shoots of rainbow pink (p<0.05). However, this was not statistically significant for Zn because of the low Zn concentration added into the contaminated soils. The results from this study indicate that applying 5 mmol EDTA kg(-1) can significantly increase the Cd, Zn, or Pb concentrations both in the soil solution or extracted using deionized water in single or combined metals-contaminated soils, thus increasing the accumulated metals concentrations in rainbow pink shoots. The proposed method worked especially well for Pb (p<0.05). The application of 2 mmol EDTA kg(-1) might too low to enhance the phytoextraction effect when used in silty clay soils.     

The Pb pollution fingerprint at Lochnagar: the historical record and current status of Pb isotopes

Ratios of 206Pb/207Pb in a Lochnagar sediment core slowly decline from c. 1.32 at 140 cm to c. 1.23 at 9 cm, and then rapidly decline to c. 1.15 at the surface. Ninety percent of the Pb in the surface sediments can be attributed to anthropogenic sources. The 206Pb/207Pb ratio data imply that catchment peat surface contains a higher fraction of anthropogenic Pb than the sediment surface. The 206Pb/207Pb ratios in the surface of the sediment core are consistent with ratios in trapped sediments collected annually between 1998 and 2003. However, there is no significant decline in these recent samples suggesting that the reduction in atmospheric Pb emissions has not yet been recorded by the sediments due to Pb inputs from the catchment. As catchment peats store about 840 kg previously deposited anthropogenic Pb since 1860, it is likely that catchment inputs will continue to affect future 206Pb/207Pb ratios.     

A 40+ year record of Cd,Hg, Pb,and U deposition in sediments of Patroon Reservoir,Albany County,NY, USA

Sediments of the Patroon Creek watershed (33 km(2)) are known to contain significant concentrations of heavy metals derived from two industrial sites within the watershed. Mercury Refining, Inc (Mereco) has stored and recycled Hg from 1955 to the present day, and National Lead Industries (NLI) manufactured aircraft components containing Cd, Pb, and U from 1958 to 1984. Here we present the first record of heavy metal deposition as preserved in a 3-m long sediment core collected in 1999 from Patroon Reservoir, a small water body (1.3 ha) downstream of the industrial sites. Bulk sediment samples were collected from the core at 0.05-m intervals and analyzed for total Cd, Pb, and U by ICP-MS and total Hg by CVAAS. Total Hg increases from less than 1 mg kg(-1) (dw) below 1.68 m, to a maximum of 6.2 mg kg(-1) at 0.80 m, and then declines to the sediment-water interface. Total Cd, Pb, and U concentrations increase abruptly above 1.68 m to maximum values of 25, 320, and 3600 mg kg(-1) (dw), respectively, and then decline gradually upwards. By correlating metal profiles with industrial history, we conclude that the 1.68 m horizon was deposited no earlier than 1958, the beginning of aircraft component manufacturing at NLI. The average, apparent sedimentation rate within the reservoir has a minimum value of approximately 0.04 m year(-1) for the 41-year period from 1958 to 1999. In the interval 0--1.68 m, average concentrations of Cd, Hg, Pb, and U are 1.69, 1.50, 461, and 13 mg kg(-1), respectively. These levels are comparable with other lake, reservoir and stream sediments that have been moderately to severely impacted by industrial pollution and are above levels expected to be detrimental to aquatic organisms.     

Sediments as monitors of heavy metal contamination in the Ave river basin (Portugal): multivariate analysis of data

The concentrations of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) were determined in river sediments collected at the Ave river basin (Portugal) to obtain a general classification scenery of the pollution in this highly polluted region. Multivariate data analysis techniques of clustering, principal components and eigenvector projections were used in this classification. Five general areas with different polluting characteristics were detected and several individual heavy metal concentration abnormalities were detected in restricted areas. A good correlation between the overall metal contamination determined by multivariate analysis and metal pollution indexes for all sampling stations was obtained. Some preliminary experiments showed that the metal concentrations normalised to the volatile matter content in the sediment fraction with grain size <63 microm seems to be an adequate method for assessing metal pollution.     

Trace metals and organochlorines in sediments near a major ocean outfall on a high energy continental margin (Sydney, Australia)

Sewage effluent from a large ocean outfall south of Sydney, southeastern Australia, is efficiently dispersed on this high energy continental margin. An enrichment of Ag, Cu, Pb and Zn is only detectable in the fine fraction (<62.5 microm) of sediment. Ag, Co, Cu, Ni, Pb and Zn in the bulk sample correlate strongly with the mud content of surficial sediment, making an identification of the anthropogenic trace metal source difficult using total sediment analyses. The concentrations of HCB and DDE in the total sediment are also slightly elevated near the outfall. In the vicinity of the outfall, the estimated sewage component in the fine fraction of sediment, using Ag, Cu and Zn in a conservative, two-endmember physical mixing model, is <5% and is <0.25% of the total sediment. A greater anthropogenic Pb component in the fine fraction (mean: 24.8%) of surficial sediment compared to Ag, Cu and Zn may suggest a source other than sewage to Sydney continental margin sediments.     

The dispersal and storage of sediment-associated metals in an arid river system: the Leichhardt River, Mount Isa, Queensland, Australia

This paper details the distribution of Cu, Pb and Zn in aquatic systems draining Mount Isa Ag-Cu-Pb-Zn Mine in arid northern Queensland, Australia. Sediment-metal concentrations in the <2mm grain-size fraction adjacent to and downstream of the mine significantly exceed background concentrations (Cu, 159; Pb, 36; Zn, 86 ppm) as well as Australian government sediment quality low trigger guidelines (Cu, 65; Pb, 50; Zn, 200 ppm). Overbank sediments are more contaminated than channel sediments with mean values of Cu, 480; Pb, 540; Zn, 750 ppm. Mean concentrations in cut riverbank samples from the <2mm fraction were Cu, 195; Pb, 724; Zn, 807 ppm. Corresponding <180 microm samples returned concentrations of Cu, 321; Pb, 995; Zn, 1110 ppm. Delivery of contaminants during wet seasons from Mount Isa Mine and historically contaminated riverbanks remains an ongoing issue. The ease of dust entrainment in arid zones means that sediments enriched in toxic concentrations of metals may be widely dispersed and ultimately ingested and absorbed by biota.     

An ozone flux-response relationship for wheat

The concentrations of heavy metals in the fine fraction (<63 microm) of 19 surficial sediment samples from the border region of Baja California (Mexico) and California (USA) were determined. The concentration ranges (in microg g(-1)) of the metals were: Cu, 4.9-23; Zn, 39-188; Ni, 16-44; Cr, 56-802; Pb, 6-21; Cd, 0.08-0.64; Ag, 0.01-0.28; and Mn, 392-1506; the intervals (percentage) for Fe and Al were 1.36-4.6 and 3.61-8.55, respectively. The heavy metals in these sediments indicate a relative enrichment of Cr (>3000%), Zn (>350%), Ni (>300%) and Cu (>150%) off the wastewater outfall at Punta Bandera in Tijuana, Baja California, with respect to non-polluted sediments of the region. Pb, Cd and Ag have low concentrations off the same outfall and enrichment factors are generally lower than 300% (Pb) and lower than 150% (Cd and Ag). This suggests that these metals have a different origin, or that they are controlled by a different geochemical mechanism than the former. The concentrations of Mn, Fe and Al occurred within ranges typical for coastal areas and probably reflect the mineralogical composition of the sediments of the region.