Particulate Pb Research Articles

Estuary-ria exchange of cadmium, lead and zinc in the coastal system of the Ria of Vigo (NW Iberian Peninsula)

Little research has been done on the land-sea exchange of trace elements, which is particularly applicable to ria coasts. In particular, trace metal enrichment in the inner part of the Ria of Vigo (the San Simon Inlet) has been observed from sediment studies but there is no information about Cd, Pb and Zn fluxes through the Rande Strait, which is the natural boundary of the estuary-ria water exchange. In order to assess metal exchanges in a ria-type system, six sampling cruises on board the R/V Mytilus (IIM-CSIC) were carried out. Water column profiles of salinity, temperature and tidal currents were obtained every 30 min. The water column for dissolved and particulate metals was sampled every two hours over a complete tidal cycle. Dissolved metal concentrations were 0.01–0.18 nM for Cd, 0.5-1.9 nM for Pb and 4-44 nM for Zn. Compared with Zn (16±12%) and especially with Cd (5.4±5.0%), particulate metal represented a significant fraction of the total concentration for Pb (41±21%). Net fluxes of dissolved Cd and Zn are higher than in the particulate phase, whereas for Pb an inverse situation was observed. The net metal exchange in the Vigo estuary-ria environment was not seasonally controlled. Dissolved Cd and Pb were driven by tidal ranges and particulate Pb by the Oitaven River flow. On the other hand, Zn did not show a defined trend. The budgets obtained for the Ria of Vigo, with the exception of Pb, were one or two orders of magnitude lower than those measured in other large European estuaries.

Lead Concentrations in Zooplankton, Water, and Particulate Matter of a Southwestern Atlantic Temperate Estuary (Argentina)

This study presents for the first time valuable results of lead (Pb) accumulation in zooplankton from a southwestern Atlantic temperate estuary, the Bahía Blanca estuary, one of the most important and industrialized coastal environments of Argentina. It considers Pb concentrations in zooplankton organisms as well as in the dissolved and particulate phases. These fractions were analyzed on account of their important role in the biogeochemical cycles of trace elements in estuarine environments. In addition, the major physicochemical variables, i.e., nutrients, and pigment concentrations, and zooplankton composition and abundance, were also considered to understand Pb levels in the above-mentioned fractions. Samplings were performed from March to December 2005 with a bimonthly frequency and comprised a study area with stations located near industrial settlements and other stations a few kilometers far from these points. The results of the physicochemical variables and nutrients and pigments agreed with historic values for the estuary and did not present any evidence of abnormalities. Dissolved Pb presented a mean concentration of 2.15±0.46μgL(-1), whereas particulate Pb presented a mean concentration of 13.52±3.07μgg(-1) dry weight (dw). In the mesozooplankton, represented by copepods, the mean concentration was similar to the particulate fraction (13.38±4.41μgg(-1) dw), whereas in the macrozooplankton, represented by mysids, it was lower (9.81±1.89μgg(-1) dw). Thus, Pb concentrations were relatively high in the dissolved and particulate phases. Moreover, zooplankton accumulated important concentrations of this metal, which was mainly incorporated through suspended particulate matter (SPM). The source of Pb in all of these fractions is related to the industry discharges as well domestic sewage located near the sampling stations. Finally, through these results, it was possible to show the importance of zooplankton and SPM in the biogeochemical cycle of Pb as well as the interaction between these fractions in an estuarine and anthropogenic environment, such as the Bahía Blanca estuary.

Biogeochemistry of Lead in the Eastern Arabian Sea and Western Bay of Bengal

Biogeochemical cycling of lead (Pb) within the Indian Exclusive Economic Zone of the Arabian Sea and Bay of Bengal was examined in terms of the dissolved and particulate Pb concentration profiles. The relative distribution of Pb between the dissolved and particulate phases were found identical to the two regions, with elevated surface concentrations derived from anthropogenic sources and low concentrations at depth due to particle scavenging. Higher industrial emissions from the Indian west coast resulted to 2.5 fold enrichment of Pb throughout the water column of the Arabian Sea in comparison to the Bay of Bengal.

Determination of particulate lead using aerosol mass spectrometry: MILAGRO/MCMA-2006 observations

Abstract. We report the first measurements of particulate lead (Pb) from Aerodyne Aerosol Mass Spectrometers, which were deployed in and around Mexico City during the Megacity Initiative: Local and Global Research Observations (MILAGRO)/Mexico City Metropolitan Area 2006 (MCMA-2006) field campaigns. The high resolution mass spectrometer of one of the AMS instruments (HR-AMS) and the measured isotopic ratios unequivocally prove the detection of Pb in ambient particles. A substantial fraction of the lead evaporated slowly from the vaporizer of the instruments, which is indicative of species with low volatility at 600 °C. A model was developed in order to estimate the ambient particulate Pb entering the AMS from the signals in the "open" and the "closed" (or "background") mass spectrum modes of the AMS. The model suggests the presence of at least two lead fractions with ~25% of the Pb signal exhibiting rapid evaporation (1/e decay constant, τ<0.1 s) and ~75% exhibiting slow evaporation (τ~2.4 min) at the T0 urban supersite and a different fraction (70% prompt and 30% slow evaporation) at a site northwest from the metropolitan area (PEMEX site). From laboratory experiments with pure Pb(NO3)2 particles, we estimated that the Pb ionization efficiency relative to nitrate (RIEPb) is 0.5. Comparison of time series of AMS Pb with other measurements carried out at the T0 supersite during MILAGRO (using Proton Induced X-ray Emission (PIXE), Inductively-Coupled Plasma Mass Spectrometry (ICP-MS) and single-particle counts from an Aerosol Time-of-Fight Mass Spectrometer (ATOFMS)) shows similar levels (for PIXE and ICP-MS) and substantial correlation. During part of the campaign, sampling at T0 was alternated every 10 min with an Aerosol Concentrator, which enabled the detection of signals for PbCl+ and PbS+ ions. PbS+ displays the signature of a slowly evaporating species, while PbCl+ appears to arise only from fast evaporation, which is likely due to the higher vapor pressure of the compounds generating PbCl+. This is consistent with the evaporation model results. Levels of particulate Pb measured at T0 were similar to previous studies in Mexico City. Pb shows a diurnal cycle with a maximum in the early morning, which is typical of primary urban pollutants. Pb shows correlation with Zn, consistent with previous studies, while the sources of Pb appear to be at least partially disjoint from those of particulate chloride. Back trajectory analysis of the T0 Pb data suggests the presence of sources inside the urban area SSW and N of T0, with different chemical forms of Pb being associated with different source locations. High signals due to particulate lead were also detected in the PEMEX site; again, no correlation between Pb and chloride plumes was observed, suggesting mostly different sources for both species.

Three-dimensional modeling of Cu and Pb distributions in Boston Harbor, Massachusetts and Cape Cod Bays

The transport and distribution of dissolved Cu (Cu diss) and Pb (Pb diss) in Boston Harbor (BH), Massachusetts Bay (MB) and Cape Cod Bay (CCB) were simulated using an existing three-dimensional hydrodynamic model. Treatment of Cu diss as a conservative tracer produced model results in good agreement with observational data in MB and CCB. Pb diss was modeled as a non-conservative tracer using particulate organic carbon (POC) extracted from a water quality model as the sorption and scavenging matrix for particulate Pb. Despite cessation of discharge from a major treatment plant in 2000 and concurrent reduction in metal loading, Cu diss and Pb diss concentrations in the Harbor remained relatively unchanged between 1998 and 2002. In contrast model results produced water column concentrations in Boston Harbor that were about 10% of the observed current standing stock of Cu diss and only about 20% of Pb diss in 2002. Both field observations and model results incorporating Cu and Pb benthic fluxes suggest that release of these metals from the previously contaminated sediments of the Harbor is now the major source of these metals to the Harbor.

Reactivity between PbSO 4 and CaCO 3 particles relevant to the modification of mineral particles and chemical forms of Pb in particles sampled at two remote sites during an Asian dust event

During the transboundary transport of anthropogenic heavy metals by mineral particles providing reaction sites, the divalent metal salt PbSO 4 can be converted to PbCO 3 in the presence of water. We carried out laboratory experiments to study the transformation process under various conditions by incorporating test particles comprising CaCO 3 of a particulate mineral component, PbSO 4, and NaCl. After the immersion of PbSO 4 particles in contact with CaCO 3 particles in a water droplet, the conversion of PbSO 4 into PbCO 3 was confirmed by the change in morphology of the original particles to stick or needle form; the percentages of the chemical forms relative to the total Pb were determined by X-ray absorption near edge structure (XANES) analysis. Approximately 60–80% of PbSO 4 was converted to PbCO 3 after 24 h. A small amount of stick particles was detected when NaCl particles attached to PbSO 4/CaCO 3 particles were exposed to air with a relative humidity (RH) of 80–90% for 24 h. XANES measurements of the samples revealed that the molar percentage of PbCO 3 relative to the total Pb content was 4%. Field experiments were also conducted to determine the chemical forms of the Pb particles during the Kosa (Asian dust storm) event. Samples were collected from two remote sites in Japan and Korea. The mass size distribution of Pb aerosols collected in Japan was bimodal with two peaks in the coarse mode; the enrichment factor of Pb suggested that its source was anthropogenic. Pb L3 edge XANES measurements of both samples indicated that they had similar shapes. These measurements also indicated that the major Pb components for the samples collected in Japan were PbO, PbSO 4 PbCl 2, and PbCO 3, with molar percentages of 44%, 30%, 21%, and 5%, respectively. No significant differences were found between the component ratios of the samples collected in Japan and Korea, suggesting that definite transformation did not occur during the transport of the Kosa particles from Korea to Japan. On the basis of these observations, we postulate that the transformation process either occurred mainly before the particles arrived at Korea or did not take place after the particles left continental Asia.

Water-Quality Diagnosis and Metal Distribution in a Strongly Polluted Zone of Deûle River (Northern France)

Using ICP-AES and ICP-MS, several metals were analyzed in water and suspended particulate matter (SPM) samples collected under normal turbidity conditions at various stations from Deule river (in northern France) to assess the impact of a former smelting plant on the fate of particulate elements and on the water quality in this aquatic environment. Compared to their regional background, particulate Pb, Zn and Cd were found to be most enriched, suggesting anthropogenic inputs from bed sediments into the water column mainly due to physical disturbances induced by barges traffics. Conversely, no significant enrichments of particulate metals such as Cu, Cr and Ni were observed in Deule SPM. Characterization of SPM with analyses of mineralogical and chemical compositions—using environmental scanning electron microscopy equipped with an energy dispersive X-ray spectrometer (ESEM/EDS)—indicated the presence of micro-specimens attributed to anthropogenic minerals, mostly PbS and ZnS. The calculated enrichment index (or the geoaccumulation index, Igeo), enrichment factor (EF) and the partition coefficient (Kd) confirmed that SPM was strongly polluted in cadmium, lead and zinc, moderately polluted in copper and unpolluted in chromium and nickel. Based on the analytical data obtained for SPM from the BCR (European Community Bureau of Reference) sequential extraction scheme, it was concluded that: (i) the reducible phases were largely more important for the binding of Pb and Cd than that of Zn and Ni and in a lesser extent Cu and Cr; (ii) copper was found to be mostly associated with the sulphides/organics fraction; (iii) chromium with a lithogenic origin was extracted in the largest percentage in the residual phase; and (iv) zinc was bound to the exchangeable-carbonate phase in the largest percentage in the particles analysed, followed by nickel and cadmium, suggesting that these metals might be easily remobilized if changes in environmental conditions would occur.

Short‐lived radionuclides (7Be and 210Pb) as tracers of particle dynamics in a river system in southeast Michigan

Riverine water samples (dissolved and particulate), surficial bottom sediments, and trapped sediments were collected mostly monthly from three stations along the Clinton River, in southeastern Michigan, over a period of ~1 yr and analyzed for 7Be and 210Pb to elucidate the types and rates of processes affecting particle dynamics in a riverine system. Using a simple irreversible scavenging box model approach, sources and sinks for dissolved and particulate 7Be and 210Pb were quantified to estimate their residence times in the dissolved and particulate phases. Resuspension rates of surficial bottom sediments calculated from the mass balance of particulate 7Be varied from 0.50 to 1.34 (geometric mean: 0.83 ± 0.34) g cm−2 yr−1, while corresponding values varied from 0.16 to 1.48 (GM: 0.38 ± 0.38) g cm−2 yr−1 using particulate 210Pb. Based on the 210Pb mass balance, it appears that only ∼2% of 210Pb was derived from direct atmospheric deposition, while ∼98% was derived from resuspension of bottom sediments. Additionally, there was a large discrepancy between mass flux collected in the trap (GM: 8.9 g cm−2 yr−1) compared to net sediment accumulation rates (GM: 0.88 ± 0.38 g cm−2 yr−1), which was attributed to sediment resuspension; this may provide insight into the frequency of particle‐recycling events. Furthermore, desorption of particle‐reactive species during resuspension events could result in the mobility of contaminants to farther distances from the contaminated site. Therefore, this study has direct relevance to the uptake of particle‐reactive species in a riverine system and thereby the water quality of rivers.

From suspended particles to strata: The fate of terrestrial substances in the Gaoping (Kaoping) submarine canyon

The river–sea system consisting of the Gaoping (new spelling according to the latest government's directive, formerly spelled Kaoping) River (KPR), shelf, and Submarine Canyon (KPRSC) located off southern Taiwan is an ideal natural laboratory to study the source, pathway, transport, and fate of terrestrial substances. In 2004 during the flood season of the KPR, a system-wide comprehensive field experiment was conducted to investigate particle dynamics from a source-to-sink perspective in the KPRSC with the emphasis on the effect of particle size on the transport, settling, and sedimentation along the pathway. This paper reports the findings from (1) two sediment trap moorings each configured with a Technicap PPS 3/3 sediment trap, and an acoustic current meter (Aquadopp); (2) concurrent hydrographic profiling and water sampling was conducted over 8 h next to the sediment trap moorings; and (3) box-coring in the head region of the submarine canyon near the mooring sites. Particle samples from sediment traps were analyzed for mass fluxes, grain-size composition, total organic carbon (TOC) and nitrogen (TN), organic matter (OM), carbonate, biogenic opal, polycyclic aromatic hydrocarbon (PAH), lithogenic silica and aluminum, and foraminiferal abundance. Samples from box cores were analyzed for grain-size distribution, TOC, particulate organic matter (POM), carbonate, biogenic opal, water content, and 210Pb ex. Water samples were filtered through 500, 250, 63, 10 µm sieves and 0.4 µm filter for the suspended sediment concentration of different size-classes. Results show that the river and shelf do not supply all the suspended particles near the canyon floor. The estimated mass flux near the canyon floor exceeds 800 g/m 2/day, whose values are 2–7 times higher than those at the upper rim of the canyon. Most of the suspended particles in the canyon are fine-grained (finer than medium silt) lithogenic sediments whose percentages are 90.2% at the upper rim and 93.6% in the deeper part of the canyon. As suspended particles settle through the canyon, their size-composition shows a downward fining trend. The average percentage of clay-to-fine-silt particles (0.4–10 µm) in the water samples increases from 22.7% above the upper rim of the canyon to 56.0% near the bottom of the canyon. Conversely, the average percentage of the sand-sized (> 63 µm) suspended particles decreases downward from 32.0% above the canyon to 12.0% in the deeper part of the canyon. Correspondingly, the substrate of the canyon is composed largely of hemipelagic lithogenic mud. Parallel to this downward fining trend is the downward decrease of concentrations of suspended nonlithogenic substances such as TOC and PAH, despite of their affinity to fine-grained particles. On the surface of the canyon, down-core variables (grain size, 210Pb ex activity, TOC, water content) near the head region of the canyon show post-depositional disturbances such as hyperpycnite and turbiditic deposits. These deposits point to the occurrences of erosion and deposition related to high-density flows such as turbidity currents, which might be an important process in submarine canyon sedimentation.

Lead pollution in subtropical ecosystems on the SE Gulf of California Coast: A study of concentrations and isotopic composition

Lead pollution was investigated in environmental matrices and biological indicators collected from two typical subtropical coastal ecosystems in the southeast Gulf of California, Mexico. Lead concentrations and isotopic compositions ( 206Pb/ 207Pb and 208Pb/ 207Pb) were measured using high resolution inductively-coupled plasma-mass spectrometry (HR-ICP-MS) and thermal ionization mass spectrometry (TIMS), respectively. Lead in surface estuary sediments (10.0–34.2 μg g −1) and particulate Pb (25.0–128.7 μg g −1, >98% of total Pb) in the water column were significantly higher than levels in natural bedrock soils (15.1 ± 8.3 μg g −1) and river runoff (1.9 ± 1.4 μg g −1). Aquatic plants had Pb concentrations between 2.5 and 7.2 μg g −1, while those in macroalgae ranged from 3 to 5 μg g −1. The ranges of mean Pb concentrations in the aquatic animals studied (ranges in μg g −1) were as follows: zooplankton 32 ± 3, mussels 2.3–3.9, oysters 1.9–7.9, snail 2.0–7.7, barnacles 0.1–18.5, fish 1.4–8.9, crab 6.3–40.2 and polychaetae 8.5–16.7. Pb values in 20–40% of oyster and fish samples and in all samples of crab exceeded acceptable levels for a food source for human consumption. Pb isotope ratios 206Pb/ 207Pb, 208Pb/ 207Pb in biota ranged from 1.188 to 1.206 and 2.448 to 2.470, respectively. A plot of 206Pb/ 207Pb versus 208Pb/ 207Pb for the environmental and biological samples collected from two study areas indicates that they contain lead from ores mined in Mexico and used in the past to produce leaded gasoline in use until 1997, natural Pb weathered from the Sierra Madre Occidental mother rock, and the later influence of inputs from a more radiogenic source related to industrial activity in the United States. Statistical software IsoSource results revealed that the Pb contained in environmental matrices and biomonitors is mostly derived from gasoline (20–90%) and US emissions (10–40%).

The effects of the San Francisco Bay plume on trace metal and nutrient distributions in the Gulf of the Farallones

The distributions of particulate elements (Al, P, Mn, Fe, Co, Cu, Zn, Cd, and Pb), dissolved trace metals (Mn, Fe, Co, Cu, Zn, and Cd), and dissolved nutrients (nitrate, phosphate, and silicic acid) were investigated in the Gulf of the Farallones, a region of high productivity that is driven by the dynamic mixing of the San Francisco Bay plume, upwelled waters, and California coastal surface waters. Particulate metals were separated into >10 and 0.4–10μm size-fractions and further fractionated into leachable (operationally defined with a 25% acetic acid leach) and refractory particulate concentrations. Dissolved metals (< 0.4μm pore-size filtrate) were separated into colloidal (0.03–0.4μm) and soluble (<0.03μm) fractions. The percent leachable particulate fractions ranged from 2% to 99% of the total particulate concentration for these metals with Mn and Cd being predominantly leachable and Fe and Al being predominantly refractory. The leachable particulate Pb concentration was associated primarily with suspended sediments from San Francisco Bay and was a tracer of the plume in coastal waters. The particulate trace metal data suggest that the leachable fraction was an available source of trace metal micronutrients to the primary productivity in coastal waters. The dissolved trace metals in the San Francisco Bay plume and freshly upwelled surface waters were similar in concentration, with the exception of Cu and Co, which exhibited relatively high concentrations in plume waters and served as tracers of this water mass. The dissolved data and estimates of the plume dynamics suggest that the impact of anthropogenic inputs of nutrients and trace metals in the San Francisco Bay plume contributes substantially to the concentrations found in the Gulf of the Farallones (10–50% of estimated upwelled flux values), but does not greatly disrupt the natural stoichiometric balance of trace metal and nutrient elements within coastal waters given the similarity in concentrations to sources in upwelled water. In all, the data from this study demonstrate that the flux of dissolved nutrients and bioactive trace metals from the San Francisco Bay plume contribute to the high and relatively constant phytoplankton biomass observed in the Gulf of the Farallones.

Identification of Pb sources in Yellow Sea sediments using stable Pb isotope ratios

Rapid economic developments in East Asian countries have inevitably resulted in environmental degradation in the surrounding seas, and concern for both the environment and protection from pollutants is increasing. Identification of sources of contaminants is essential to environmental pollution management. In this study, the provenance of anthropogenic lead (Pb), a major pollutant of Yellow Sea sediments, was determined for river mouth sediments, including those of the Changjiang, Huanghe, Han, and Geum Rivers, and for age-determined shelf core sediments through the measurement of Pb isotope ratios in the HCl-leached fraction using multi-collector inductively coupled plasma-mass spectrometry (MC ICP/MS). Anthropogenic Pb has accumulated in shelf core sediments since 1910, and its isotope ratios were estimated as 0.863–0.866 and 2.119–2.125 for 207Pb/ 206Pb and 208Pb/ 206Pb, respectively, from the mixing relationships of the two endmembers. River mouth sediments exhibited enough distinction in anthropogenic Pb isotope ratios to be discriminated: 0.874 (2.144) in the Huanghe, 0.856 (2.129) in the Han, 0.857 (2.122) in the Geum, and 0.854 (2.101) in the Changjiang for 207Pb/ 206Pb ( 208Pb/ 206Pb), respectively. Although isotope ratios of geogenic Pb in sediments dating before 1910 showed narrow ranges (0.842–0.845 and 2.088–2.100 for 207Pb/ 206Pb and 208Pb/ 206Pb, respectively), distinct isotope ratios in each core permitted source identification of sediments in the Yellow Sea based on geographic locations and the geogenic Pb of each river. By comparing the isotope ratios of the estimated anthropogenic Pb to source-related materials, the provenances of anthropogenic Pb in Chinese river sediments were presumed to be Chinese coal or ore, which is also a major source of atmospheric particulate Pb. The anthropogenic Pb in the shelf core sediments in the northern Yellow Sea originated from northern Chinese cities such as Beijing and Tianjin through atmospheric pathways. Pb isotope ratios indicated that Pb in Korean river sediments was characteristic of local Korean ores.

210Pb and 230Th in settling particles in the western Northwest Pacific Ocean: Particle flux and scavenging

A mooring of three conical time-series sediment traps was deployed at two sites in the western Northwest Pacific Ocean for 9 months. Total mass fluxes and activities of 210Pb and 230Th were determined for the settling particles to elucidate their scavenging and transport processes. Sediment samples also were analyzed for 210Pb activities. Total mass fluxes, 210Pb fluxes and 230Th fluxes showed large seasonal variations and their weighted mean fluxes tended to increase with depth, with an especially large increase near-bottom. The ratios of the observed 210Pb fluxes to the 210Pb deficiency fluxes in the upper traps at the two sites were only 0.02 and 0.12, and were attributable to advective export of 210Pb from the surface waters. Those ratios in the near-bottom traps ranged between 1.22 and 2.63. This suggests that these high ratios are due to effective particle scavenging, large lateral 210Pb import and input of resuspended particles that have not become incorporated into the sediments. The mean total 230Th fluxes at the near-bottom traps were 4.2–6.7 times higher than that expected from production in the overlying water column. The 210Pb activities in the surficial sediments were much lower than those in the near-bottom traps. The 210Pb accumulation rates estimated from the excess 210Pb inventory in the sediment column were 40–70% higher than the mean 210Pb fluxes at the near-bottom traps. The ratios of the 210Pb accumulation rates to the 210Pb deficiency fluxes at the near-bottom traps ranged between 2.0 and 3.7. The high fluxes of particulate 210Pb and 230Th at the near-bottom traps reflected a combination of enhanced scavenging of dissolved nuclides and the lateral redistribution of particulate matter by downslope and alongshore transports. However, it was not possible to discriminate among the various processes contributing to high nuclide fluxes.

The role of wildfire and gully erosion in particulate Pb export from contaminated peatland catchments in the southern Pennines, U.K.

The near-surface layer of peatlands of the Peak District, southern Pennines, UK, is severely contaminated with atmospherically deposited Pb. Contemporary catchment soil Pb inventories at Upper North Grain and Torside Clough reveal that ∼ 23% and ∼ 54%, respectively, of the potential store of Pb in each catchment has been lost through erosion of the contaminated near-surface peat layer. Soil Pb inventories and the Pb content of suspended sediments reveal that, in both catchments, the main mechanism for contemporary particulate Pb export is gully erosion. Historical sheet erosion on bare peat flats at Torside Clough has released significant quantities of Pb into the fluvial system, triggered by the exposure of the near-surface peat during an accidental wildfire in 1970. Up to 32% of the total Pb export from the catchment may have been released during a discrete erosion event soon after the wildfire. Accidental wildfires and the subsequent release of highly contaminated peat into the southern Pennine fluvial system may increase under predicted climate change scenarios.

Effects of Pb and Cu additives on microstructure and wear corrosion resistance behaviour of PM Al–Si alloys

The wear and wear corrosion resistance of Al–20Si–XPb–YCu (X=0–10 wt-%, Y=0–3 wt-%) alloys fabricated using powder metallurgy technique and subsequent heat treatments were evaluated using a block on ring tribotest. The microstructures of all aluminium alloys were observed using an optical microscope, a scanning electron microscope and an X-ray energy dispersive spectroscope. The evaluation studied the effects of applied potential and environments of dry air and 3·5 wt-%NaCl aqueous solution. The microstructural analysis showed that Pb was bimodally distributed in Pb containing alloys, and Cu particles formed the intermetallic phase CuAl2. Additionally, the hardness of both Pb and Cu containing alloys increased significantly. The wear and corrosion results showed that the addition of both lead (Pb) and copper (Cu) increased the wear resistance and the corrosion rate, while heat treatments reduced the corrosion rate of most alloys except the Al–Si alloy. Furthermore, comparison of all alloys following heat treatment shows that the wear corrosion resistance of Al–Si alloy is inferior to that of the other alloys. Therefore, addition of Pb and Cu further improved the wear corrosion resistance. Additionally, at anodic potential, the wear corrosion rate and current density of both Al–Si and Al–Si–Cu alloys containing particle Pb were significantly lower than those of alloys containing no Pb, because the layer produced by corrosion comprised Al, O and Pb elements.

Effects of Pb and Cu additives on microstructure and wear corrosion resistance behaviour of PM Al–Si alloys

The wear and wear corrosion resistance behaviour of Al–20Si–XPb–YCu (X=0–10 wt-%, Y=0–3 wt-%) alloys fabricated by a powder metallurgy (PM) technique and subsequent heat treatments were evaluated by a block on ring tribotest. The microstructure of all aluminium alloys was observed by optical microscopy and scanning electron microscopy with X-ray energy dispersive spectroscopy. The effects of applied potentials and environments including dry air and 3.5 wt-%NaCl aqueous solution were studied. The results of microstructure analysis indicated that Pb exhibited a bimodal distribution in the Pb containing alloys, and Cu particles become to form the intermetallic phase CuAl2. Furthermore, the hardness rises significantly for both Pb and Cu containing alloys only after solid solution quenching treatment. The wear and corrosion results showed that the addition of both lead and copper would improve the wear resistance but lead to a higher corrosion rate whereas heat treatment had a beneficial effect of reducing the corrosion rate of most alloys with the exception of Al–Si alloy. Furthermore, by comparison of all alloys after heat treatment, the wear corrosion resistance of Al–Si alloy was inferior to the other alloys; consequent additions of Pb and Cu further improved its wear corrosion resistance. Moreover, at an anodic potential, the wear corrosion rate and current density of both Al–Si and Al–Si–Cu alloys containing particle Pb decrease significantly owing to a corrosion product layer composed of Al, O and Pb elements.

Trace metals in the water column of the Vigo Ria: Offshore exchange in mid-winter conditions

Samples of dissolved and particulate trace metals were taken in January–February 1995 at four different stations through an axial transect in the water column of the Vigo Ria. Average dissolved metal concentrations were 72 ± 9 pM for Cd, 4.6 ± 1.9 nM for Cu, 24 ± 20 nM for Fe, 2.5 ± 1.3 nM for Ni, 650 ± 340 pM for Pb and 4.8 ± 2.2 nM for Zn. No important differences in dissolved concentrations between stations or trend with depth were observed. Average particulate metal concentrations were 0.24 ± 0.12 μg g −1 for Cd, 44 ± 21 μg g −1 for Cu, 33 ± 8 μg g −1 for Ni, 156 ± 112 μg g −1 for Pb and 167 ± 32 μg g −1 for Zn. Both dissolved and particulate concentrations are within ranges for other European Atlantic coastal areas. The ria–ocean metal exchange was also quantified following the LOICZ (Land–Ocean Interaction in the Coastal Zone) protocol for quasi-steady states in estuaries. The pattern obtained for this winter campaign shows four different types of metal budgets: (1) a null net exchange for Cd; (2) a net dissolved output to the ocean for Cu, Fe and Zn (1.5, 4.1 and 0.8 mmol s −1, respectively); (3) a net export for both dissolved (0.12 mmol s −1) and particulate (0.29 mmol s −1) Pb; and (4) a net accumulation of Ni in the ria, with a net incoming oceanic flux of 0.51 mmol s −1 of dissolved and 0.31 mmol s −1 of particulate metal.

Speciation of adsorbed arsenate on the surface of hydrous iron oxide

effluent is complex and is characterized by elevated concentrations of iron and sulfate, low pH, and high concentrations of a wide variety of metals depending on the host rock geology. Massive inadvertent discharges from acid mines have given rise to dramatic cases of ecological damage. These events indicate an improved understanding of the mechanism controlling metal transport to the river is irr~portant, since the aquatic ecology will be affected, to some degree, dependent on the phase (dissolved or particulate) in which the metal is transported. In this study, polluted water samples were collected along the Hengshi River near the Dabaoshan mine, Guangdong, China, in April 2005. The concentrations of dissolved Cu, Zn, Cd and Pb have been determined using ICP-MS and the chemical speciation of those metals in suspended particles was examined using BCR methods and SEM/EDX mineralogical analysis. Combining these two sets of data, the intention was to develop geochemical concepts, which explain the behavior of Cu, Zn, Cd and Pb in particle-water interactions of heavy metals in AMD. The results show that the dissolved heavy metals exhibited non-conservative behavior in the Hengshi River. The dissolved and particulate Cu, Zn, Cd and Pb have the similar spatial distribution, which decreased gradually along the fiver except in the lower reaches because of the absorption-desorption between dissolved and particulate phases. Although the metal concentrations in both phases were elevated, dissolved metals were dominant and had the maximum concentrations in the low pH region. The maximum concentrations of dissolved Cu, Zn, Cd and Pb were as high as 13.82, 50.83, 0.103 and 2.91 mg/L, respectively. These four metals displayed similar evolution trends along the river, while some different behaviors do exist. Pb decreased sharply with the rise of pH, however, Cd appeared to decrease much slower. Studies on suspended particles with chemical speciation analysis and SEM/EDX indicate that the residual speciation was the major species for those four metals in suspensions. And the reductable speciation was also high, especially Cd, which indicated that they all have potential risk to the environment.

Factor analysis of water quality characteristics including trace metal speciation in the coastal environmental system of Chennai Ennore

Statistical analysis of water quality parameters including trace metal speciation was undertaken with a view to seeing the interrelationship between different variables and also to identify probable source components in order to explain the pollution status of Chennai Ennore coastal environmental system. Factor analysis has been used in the present work. This is essentially a data reduction technique and will suggest how many variates are important to explain the observed variances in the data. The possible variances in the water quality parameters may be due to either sources of anthropogenic origin or natural variances due to the season or due to different biogeochemical processes that are taking place in the system. When this analysis was carried out with our data on water quality parameters in the above coastal environmental system, we found that the prominent factor or the first factor called the eutrophication factor explained 24.51% of the total variance (comprised of variables like DO, pH, SS, ammonia-N, phosphate and silicate). The second factor called the copper contamination factor explained 10.61% (comprised of variables like labile Cu, total Cu and particulate Cu) and the third factor called metal removal factor explained 10.11% (comprised of variables like particulate Zn, particulate Pb and water temperature) of the variances, respectively. Although there are four more factors, they are all having variances less than 10%. From this study, it is seen that eutrophication is the main source component of pollution to the surface waters of this estuary and its adjacent coastal waters compared to dissolved trace metals.

Magnetic properties and heavy metal contents of automobile emission particulates

Measurements of the magnetic properties and total contents of Cu, Cd, Pb and Fe in 30 automobile emission particulate samples indicated the presence of magnetic particles in them. The values of frequency dependent susceptibility (chi(fd)) showed the absence of superparamagnetic (SP) grains in the samples. The IRM(20 mT) (isothermal remanent magnetization at 20 mT) being linearly proportional to SIRM (saturation isothermal remanent magnetization) (R(2)=0.901), suggested that ferrimagnetic minerals were responsible for the magnetic properties of automobile emission particulates. The average contents of Cu, Cd, Pb and Fe in automobile emission particulates were 95.83, 22.14, 30.58 and 34727.31 mg/kg, respectively. Significant positive correlations exist between the magnetic parameters and the contents of Pb, Cu and Fe. The magnetic parameters of automobile emission particulates reflecting concentration of magnetic particles increased linearly with increase of Pb and Cu content, showed that the magnetic measurement could be used as a preliminary index for detection of Pb and Cu pollution.