Changes of copper speciation in maize rhizosphere soil

Chemical forms of copper in the rhizosphere and bulk soil of maize were investigated using rhizobox cultivation and sequential extraction techniques. The copper accumulations were also determined. The results demonstrated that there were continuous changes in copper fractionation within the maize rhizosphere. Initially, the amount of exchangeable copper increased before dropping below the initial level after 40 days or so. Carbonate associated copper followed a similar trend of change, but with a slower pace than the exchangeable copper. The increase in carbonate associated copper only become evident after 30 days, with the net loss occurring after 60 days. There were also initial increases in oxide bound copper as well as decreases in the organic matter associated copper, both followed by a turnover after 40-50 days. The accumulation of copper in the maize plant was found to be biomass dependent. The amount of accumulated copper absorbed in the plant material exceeded the initial quantity of the exchangeable copper in the soil, revealing a transformation from less bioavailable to more bioavailable fractions. During cultivation, decreases in redox potential and increases in pH, dissolved organic carbon (DOC), and microbial activity in the maize rhizosphere were observed. The change in copper speciation may result from root-induced changes in DOC, redox potential, and microbial activity in the rhizosphere.     

Distribution and Fractionation of Copper in Soils of Apple Orchards (5 pp)

Background Frequent application of Bordeaux mixture, which includes copper, as a fungicide in fruit and grape orchards may lead to copper accumulation in the soil, especially when orchard age and application times increase. The objectives of this study were: (i) to investigate the copper content and its spatial distribution in orchard soils; (ii) to identify the copper fractionation in soil and its relationship with plant uptake; (iii) to understand the characteristics of copper contamination in orchard soils. Materials and Methods Soil profile samples were taken in apple orchards with ages of 0, 5, 10, 20, 30 years and pot experiments were also carried out to study the effects of external copper input on copper fractionation. All soil samples were air-dried, ground and extracted with 0.43 mol L–1 HNO3 for the total absorbed copper. Fractionation determination was conducted following Tessier and Shuman sequential extraction methods, and copper was measured with AAS. Plant samples were first dry ashed, dissolved with 6 mol L–1 HCl and then copper and other elements were measured with ICP-MS.Results and Discussion Soil total Cu was higher in the apple orchards than that in non-orchard fields and was seen to have increased with orchard age. Soil Cu increased substantially with the average annual copper increase, ranging from 2.5 to 9 mg Cu kg–1. The distribution of copper in the soil profile was uneven, decreasing from surface to deeper layers, and the differences were significant, but the contents in every layer were also significantly correlated with those in the next layers. For all copper fractions, the organically bound, crystalline Mn oxide bound, and amorphous Fe bound fractions extracted with the Shuman method were much higher than the exchangeable and residual fractions. Using the Tessier method, organically bound, carbonate bound and Fe-Mn oxide bound fractions were much higher. With an increase in external copper input, the organically bound, crystalline Mn oxide bound and amorphous Fe bound fractions in the Shuman method and organically bound, carbonate bound and Fe-Mn oxide bound fractions in the Tessier method all increased significantly, while the changes in other fractions were not significant. Soil total copper and copper fractions were found to have good correlations with apple tree uptake. Copper in fruit flesh had significant correlations with soil total content in the 0–10 cm layer, all the copper fractions in the 0–5 cm layer, and some fractions in the deeper layers. Conclusion Copper content in orchard soils increased significantly with intensive application of Bordeaux mixtures and orchard age. Copper content decreased sharply from the topsoil to deeper soil layers. The copper contents in different layers also significantly correlated with those in the next layers. Dominant fractions of the copper in soil were mainly associated with organic matter, iron and manganese oxides and carbonates. A close relationship was found between the copper content in soils and in apple tree organs (which contained 8.9 to 66mg kg–1 Cu). Recommendation and Perspective Though most copper in the soil was specifically adsorbed or immobilized, and copper was mainly distributed in topsoil, which was essentially devoid of roots, the copper concentration of fruit still had significantly positive correlations with soil copper and most copper fractions. Therefore, measures must be taken to control copper accumulation in orchard soils and to make the apple fruit production sustainable.     

Copper regulation and homeostasis of Daphnia magna and Pseudokirchneriella subcapitata: influence of acclimation

This study aimed to evaluate (1) the capacity of the green alga Pseudokirchneriella subcapitata and the waterflea Daphnia magna to regulate copper when exposed to environmentally realistic copper concentrations and (2) the influence of multi-generation acclimation to these copper concentrations on copper bioaccumulation and homeostasis. Based on bioconcentration factors, active copper regulation was observed in algae up to 5 microg Cu L(-1) and in daphnids up to 35 mug Cu L(-1). Constant body copper concentrations (13+/-4 microg Cu g DW(-1)) were observed in algae exposed to 1 through 5 microg Cu L(-1) and in daphnids exposed to 1 through 12 microg Cu L(-1). At higher exposure concentrations, there was an increase in internal body copper concentration, while no increase was observed in bioconcentration factors, suggesting the presence of a storage mechanism. At copper concentrations of 100 microg Cu L(-1) (P. subcapitata) and 150 microg Cu L(-1) (D. magna), the significant increases observed in body copper concentrations and in bioconcentration factors may be related to a failure of this regulation mechanism. For both organisms, internal body copper concentrations lower than 13 microg Cu g DW(-1) may result in copper deficiency. For P. subcapitata acclimated to 0.5 and 100 microg Cu L(-1), body copper concentrations ranged (mean+/-standard deviation) between 5+/-2 microg Cu g DW(-1) and 1300+/-197 microg Cu g DW(-1), respectively. For D. magna, this value ranged between 9+/-2 microg Cu g DW(-1) and 175+/-17 microg Cu g DW(-1) for daphnids acclimated to 0.5 and 150 microg Cu L(-1). Multi-generation acclimation to copper concentrations >or =12 microg Cu L(-1) resulted in a decrease (up to 40%) in body copper concentrations for both organisms compared to the body copper concentration of the first generation. It can be concluded that there is an indication that P. subcapitata and D. magna can regulate their whole body copper concentration to maintain copper homeostasis within their optimal copper range and acclimation enhances these mechanisms.     

The characteristics of wet air oxidation of phenol over CuOx/Al2O3 catalysts: effect of copper loading

The nature of active copper species is well-known to vary with copper loading, i.e., isolated Cu(2+) to bulk CuO. In this work, however, the effect of copper loading on the activity and the selectivity was investigated for the wet oxidation of phenol over CuO(x)/Al(2)O(3) catalysts. The activity and the mineralization selectivity of the catalysts increased with copper loading up to 7wt% and remained almost the same at a higher loading. The optimum copper loading was about 7wt% for the wet oxidation of phenol over CuO(x)/Al(2)O(3) catalysts in this work. The nature of copper species with different loading was characterized with TPR, XRD, and XANES. The chemical states of copper in the CuO(x)/Al(2)O(3) catalysts were confirmed as varying with copper loading: isolated Cu(2+) ions for 1wt%; highly dispersed Cu(2+) cluster for 5wt% and 7wt%, and bulk CuO for 10-25wt%. The stability of the CuO(x)/Al(2)O(3) catalysts with different copper loading was also studied with respect to carbonaceous deposits and copper leaching.     

Bacterial stimulation of copper phytoaccumulation by bioaugmentation with rhizosphere bacteria

Copper contaminated areas pose environmental health risk to living organisms. Remediation processes are thus required for both crop production and industrial activities. This study employed bioaugmentation with copper resistant bacteria to improve phytoremediation of vineyard soils and copper mining waste contaminated with high copper concentrations. Oatmeal plant (Avena sativa L.) was used for copper phytoextraction. Three copper resistant bacterial isolates from oatmeal rhizosphere (Pseudomonas putida A1; Stenotrophomonas maltophilia A2 and Acinetobacter calcoaceticus A6) were used for the stimulation of copper phytoextraction. Two long-term copper contaminated vineyard soils (Mollisol and Inceptisol) and copper mining waste from Southern Brazil were evaluated. Oatmeal plants substantially extracted copper from vineyard soils and copper mining waste. As much as 1549 mg of Cu kg?1 dry mass was extracted from plants grown in Inceptisol soil. The vineyard Mollisol copper uptake (55 mg Cu kg?1 of dry mass) in the shoots was significantly improved upon inoculation of oatmeal plants with isolate A2 (128 mg of Cu kg?1 of shoot dry mass). Overall oatmeal plant biomass displayed higher potential of copper phytoextraction with inoculation of rhizosphere bacteria in vineyard soil to the extent that 404 and 327 g ha?1 of copper removal were respectively observed in vineyard Mollisol bioaugmented with isolate A2 (S. maltophilia) and isolate A6 (A. calcoaceticus). Results suggest potential application of bacterial stimulation of phytoaccumulation of copper for biological removal of copper from contaminated areas.     

氧化亚铁硫杆菌浸铜研究及胞外多聚物的作用

为了获得氧化亚铁硫杆菌(Acidithiobacillus ferrooxidans,A.f)以及胞外多聚物(extracellular polymeric sub-stances,EPS)对铜浸出的作用结果,进行了透析袋实验,设置2个处理,2者的浸出液均为成熟菌液,但一个将铜片装入透析袋中以隔离A.f及EPS与铜的直接接触。结果表明:(1)菌液的处理和加透析袋的处理中铜都得到了浸出,240 h铜的浸出浓度分别为6 796 mg/L和1 366 mg/L,可知A.f及EPS与铜片直接接触能促进铜的浸出;(2)透析袋的处理中Fe3+保持较高浓度,说明Fe3+与EPS络合后被阻挡在透析袋外面从而不能与铜反应,可知EPS在A.f浸铜中起了媒介载体的作用;(3)2者的SEM图表明无透析袋的处理A.f与铜在实验初期发生了吸附,实验后期则无,实验初期铜快速浸出是由于传质距离短,而后期速度变缓是由于传质距离增大。     

Influence of acidification of CCB (Cu/Cr/B) impregnated wood on fungal copper tolerance

Copper tolerant fungi are known for more than 60 years but the complete mechanisms of copper tolerance by these fungi are still not fully understood. Copper tolerance has previously been linked to oxalic acid excretion by copper tolerant brown rot fungi. The oxalic acid then reacts with copper in the wood to form an insoluble and therefore less toxic copper oxalate. It has been suggested that copper tolerance could be due to lowering of the pH of the medium rather than the low solubility of copper oxalate. In order to elucidate this presumption, copper/chromium/boron (CCB) treated wood specimens were acidified with organic (oxalic, acetic, lactic, formic) and inorganic (sulphuric) acids and exposed to copper tolerant (Antrodia vaillantii, Leucogyrophana pinastri) and copper sensitive (Poria monticola, Gloeophyllum trabeum) brown rot fungal strains according to the mini block procedure. After eight weeks of exposure, the wood specimens were isolated and their mass losses determined. Additionally, electron paramagnetic resonance (EPR) measurements on the exposed specimens were performed. The EPR spectra of the specimens decayed by A. vaillantii were very similar to the EPR spectra of the specimens acidified with oxalic acid. Additionally, acidification of the CCB impregnated specimens made them significantly more susceptible to decay by both the copper tolerant and copper sensitive brown rot fungi.     

Evaluation of factors influencing root-induced changes of copper fractionation in rhizosphere of a calcareous soil

Major factors influencing the root-induced copper fractionation changes within the rhizosphere of maize, wheat, pea, and soybean seedlings were evaluated using a contaminated calcareous soil. The effects of acidification, alkalization, and introduction of root exudates were investigated by addition of acid, alkaline and root exudates from solution cultures, prior to incubation and copper fractionation. Raw and sterilized soils were compared for changes of copper fractionation in the rhizosphere using rhizoboxes with maize, wheat, pea and soybean seedlings. The results indicated that the general trend in considerable changes was similar among the plant species studied. The rhizosphere experienced a depletion of carbonate associated and organic bound copper along with an accumulation of exchangeable and Fe-Mn oxide bound copper. The resulting significant influence of root exudates on copper fractionation appears to have been produced through complexation rather than acidification or alkalization. The increase in exchangeable copper in rhizosphere was strengthened by microorganisms.     

Effects of pH on the mortality and accumulation of copper in tissues of Oreochromis niloticus

In the present study, effect of pH on the mortality and accumulation of copper in various tissue and organs of Oreochromis niloticus were tested at varying concentrations of copper in the medium and over different periods of time. Experimental animals were exposed to pH 5.5, 7.8 and 9.5 and 0.1, 0.5, 1.0 and 5.0 ppm copper over periods of 7, 15 and 30 days in liver, gills and muscle were determined using atomic absorption spectrophotometric techniques. The rate of mortality at 1.0 and 5.0 ppm Cu was 100% after 7 days of exposure at pH 5.5 while at 5.0 ppm Cu was 66% after 30 days of exposure at pH 7.8. No mortality was observed in any of the copper concentrations tested at pH 9.5. In all pH levels, tissue accumulation of copper increased with increasing concentrations of copper in the medium at a given exposure period. In all pH values tested, highest levels of copper were found in the liver of O. niloticus, followed by the gills and muscle tissues. Accumulation of copper in all tissues were higher at pH 5.5 compared with the other pH values in all the conditions tested.     

Influence of growth form on the accumulation of airborne copper by lichens

Lichens are known to accumulate airborne elements. This characteristic makes them useful as biomonitors of air quality. However, direct correlations of element concentrations in the air with element concentrations in lichen thalli are generally unavailable. The purpose of this study was to quantitatively examine the relationship between concentrations of copper in ambient air samples and thalli of foliose and fruticose lichens. Lichen samples from four sites along an air copper gradient were collected and analyzed. Foliose specimens consistently accumulated more than twice as much copper as fruticose specimens at all four sites. The relationship between copper concentrations in foliose and fruticose lichens and ambient air samples along an airborne copper gradient was examined using a stepwise regression model. An R² value of (0.84) and an F-statistic of (182.5, p<0.001) for the model indicate that variability in lichen copper concentrations between sites is explained by airborne copper concentrations. Based on the regression analysis both foliose and fruticose growth forms appear to accurately predict airborne copper concentrations. A significant interaction between the airborne copper and growth form variables and large differences in the calculated slopes suggests that foliose lichens more efficiently accumulate airborne copper than fruticose lichens.     

Some effect of CuSO4 on carp

Abstract Copper treatment, muscle and liver accumulate a great amount of copper ions. The higher concentration of copper ions in the organism caused an elevated level of metallothionein. Copper induced the synthesis of metallothionein, mostly in the livers. In gel chromatography heat stable low molecular weight protein certain coming from the destruction of high molecular weight proteins could be observed. On the effect of higher copper ion concentration in the liver, the level of the metallothionein bound to copper (as related to total protein bounded to copper) was decreased. This phenomenon shows the weaker affinity of apothionein to copper, compared to other proteins.

Follows copper sulphate treatment, every measured blood serum parameter was changed. GOT activity rose to 130% and the GPT to 300% of control. LDH activity increased, too. According to this, the anaerobic way became preferred in glucose metabolism. On the effect of copper sulphate stress the blood serum glucose concentration was higher than the control value.     

Leaching behavior and chemical stability of copper butyl xanthate complex under acidic conditions

Although xanthate addition can be used for treating copper-containing wastewater, a better understanding of the leaching toxicity and the stability characteristics of the copper xanthate complexes formed is essential. This work was undertaken to evaluate the leaching behavior of copper xanthate complex precipitates by means of toxicity characteristics leaching procedure (TCLP) and semi-dynamic leaching test (SDLT) using 1 N acetic acid solution as the leachant. Also, the chemical stability of the copper xanthate complex during extraction has been examined with the studying of variation of chemical structure using UV-vis, Fourier transform infrared and X-ray photoelectron spectroscopies (XPS).Both TCLP and SDLT results showed that a negligible amount of copper ion was leached out from the copper xanthate complex precipitate, indicating that the complex exhibited a high degree of copper leaching stability under acidic conditions. Nevertheless, chemical structure of the copper xanthate complex precipitate varied during the leaching tests. XPS data suggested that the copper xanthate complex initially contained both cupric and cuprous xanthate, but the unstable cupric xanthate change to the cuprous form after acid extraction, indicating the cuprous xanthate to be the final stabilizing structure. Despite that, the changes of chemical structure did not induce the rapid leaching of copper from the copper xanthate complex.     

A field study of the ecotoxicology of copper to bryophytes

The impact of particulate copper, emitted from a copper rod-rolling plant, on the distribution of common grassland bryophytes has been investigated. Several areas of managed grassland, differing in total and water-extractable soil copper content, surrounding the factory were surveyed to establish species composition and distribution of the bryophyte flora. Clear differences emerged in the distribution patterns of the main acrocarpous (upright/tufted growth form) and pleurocarpous (horizontal/spreading growth form) species present, with some species being more or less confined to soils with elevated copper (Pohlia nutans), whilst others were absent from such sites. The distribution of acrocarpous species was not related to increasing soil copper concentrations, whereas pleurocarpous species showed considerable sensitivity. This may not be a simple reflection of sensitivity to copper; ecological factors such as differences in patterns of water and soluble copper uptake between the different growth forms may be significant factors, as may be changes in the vascular plant flora giving rise to differences in population densities of potential competitors between sites. Pleurocarpous species are absent from grassland where total soil copper >550 microg g(-1) dry weight, whilst the less sensitive acrocarpous species occur at total soil copper levels in excess of 2000 microg g(-1) dry weight.     

Functional recovery of biofilm bacterial communities after copper exposure

Potential of bacterial communities in biofilms to recover after copper exposure was investigated. Biofilms grown outdoor in shallow water on glass dishes were exposed in the laboratory to 0.6, 2.1, 6.8 micromol/l copper amended surface water and a reference and subsequently to un-amended surface water. Transitions of bacterial communities were characterised with denaturing gradient gel electrophoresis (DGGE) and community-level physiological profiles (CLPP). Exposure to 6.8 micromol/l copper provoked distinct changes in DGGE profiles of bacterial consortia, which did not reverse upon copper depuration. Exposure to 2.1 and 6.8 micromol/l copper was found to induce marked changes in CLPP of bacterial communities that proved to be reversible during copper depuration. Furthermore, copper exposure induced the development of copper-tolerance, which was partially lost during depuration. It is concluded that bacterial communities exposed to copper contaminated water for a period of 26 days are capable to restore their metabolic attributes after introduction of unpolluted water in aquaria for 28 days.     

Desorption of copper and cadmium from soils enhanced by organic acids

The adsorption/desorption behavior of copper and cadmium on soils was investigated in this study. The adsorption isotherm of copper and cadmium conformed to Langmuir equation better than Freundlich equation. The effect of ionic strength, pH, and organic acid, including ethylenediamine tetraacetic disodium acid salt (EDTA), citric acid, oxalic acid and tartaric acid, on the desorption of copper and cadmium was studied. The desorption of copper and cadmium increased with the increase of ionic strength, while the desorption decreased with the rise of pH. The desorption of copper and cadmium enhanced by organic acids was influenced by pH. EDTA showed excellent enhancement on the desorption of both copper and cadmium; citric acid demonstrated great enhancement on the desorption of copper but negligible enhancement on the desorption of cadmium; oxalic acid enhanced the desorption of copper only at pH around 6.4 and enhanced the desorption of cadmium in the pH range from 6.4 to 10.7; tartaric acid slightly enhanced the desorption of copper but negligibly enhanced the desorption of cadmium. The desorption mechanism in the presence of organic acids were explained as the competition of complexation, adsorption and precipitation. The net effect determined the desorption efficiency. This study provided guidance for the selection of organic acids to enhance the electrokinetic (EK) remediation of copper and cadmium from contaminated soils.     

Patterns of soil copper contamination and temporal changes in vegetation in the vicinity of a copper rod rolling factory

Patterns of soil copper contamination have been examined in the vicinity of a copper rod rolling plant in Prescot, Merseyside, UK. The site, established in 1975, was found to possess clear patterns of soil copper contamination, with the highest levels of HNO3 and water-extractable fractions encountered in the factory grounds adjacent to the location of the furnace chimney. The majority of the copper had accumulated in the upper soil horizons. The site is surrounded by planted lawns, established at different times after the commissioning of the plant. The species composition of the extant grassland communities, found at sites with differing soil copper levels, was compared to the composition of the original seed mixtures sown at each of ten sites. These surveys clearly showed that different levels of soil copper contamination had produced significant changes in grassland composition with time. At the most polluted site, copper tolerant Agrostis capillaris clones were the main grasses present only two years after the area was sown with a four-species mixture of non-tolerant grass seed. Lolium perenne possessed extreme sensitivity to copper. A number of dicotyledonous species, normally considered sensitive to elevated copper levels, were found to be unaffected where such conditions had arisen after plants had established from seed.     

Depuration of copper and zinc by green oysters and blue mussels of Taiwan

This paper describes depuration processes of copper and zinc in green oysters (Crassostrea gigas) and in blue mussels (Mytilus smarangdium) collected from an environment with heavy copper contamination, and then transferred to natural clean seawater. Results show that the total loss of copper content per oyster is an exponential function of exposure time for the first 6 days with a depuration rate of 351 microg g(-1) day(-1) and then levels off. During this exponential decrease period approximately 67% of the copper accumulated in green oysters was depurated. However, when the copper contents in the oysters decreased from 2225 +/- 111 microg g(-1) to 344 +/- 18.7 microg g(-1) the depuration rates decreased from 245 microg g(-1) day(-1) to 0.08 microg g(-1) day(-1). This means that green oysters had a 16-fold higher copper depuration rate (351 microg g(-1) day(-1)) than normal oysters (21.5 microg g(-1) day(-1)) for the first 6 days. However, the depuration of accumulated copper and zinc by the mussels was a fast process in natural clean seawater. About 91% of the accumulated copper was lost during the first 6-day period; copper contents declined from 20.2 +/- 3.41 microg g(-1) to 1.80 +/- 0.21 microg g(-1). Only 36% of the accumulated zinc was lost during a depuration period of 6 days. Calculations show that the biological half-lives of copper in green and normal oysters were 11.6 and 25.1 days, respectively. The biological half-lives of zinc in green and normal oysters were 16.7 and 30.1 days, respectively. In spite of the relatively low initial copper content in blue mussels being 20.2 +/- 3.41 microg g(-1), the biological half-life is only 6.40 days. From these results it is important to emphasise that the fastest turnover rate is for copper in blue mussels. However, zinc is more retentive in blue mussels than copper.     

In vitro studies of copper release from powder particles in synthetic biological media

The aim of this paper is to provide quantitative data on copper release from powder particles of different copper materials, including artificial copper patina, Cu(2)O and metallic Cu, when exposed to different synthetic biological media to simulate an inhalation scenario and/or skin contact. Generated data may contribute in risk assessment of potential health effects following exposure to and handling of various copper materials. All tests were performed in vitro to determine total copper concentrations, release rates of total copper, and to elucidate its time-dependence. The copper release process was interpreted in terms of specific surface area, surface morphology-, and composition. All powder materials show a time-dependent release process with total copper release rates less than 3 microg/cm(2) per hour at steady state conditions, for all media investigated. The importance of using relevant test media when simulating different interstitial lung conditions and difficulties encountered when comparing powder particles of essentially different properties are thoroughly discussed.     

Circulation of copper in the biotic compartments of a freshwater dammed reservoir

This study concerns a chronic copper release in an aquatic ecosystem: Mirgenbach reservoir; which is characterized by high salinity, conductivity and hardness, a eutrophic state and a high temperature. To study the bioavailability of copper in the biotic compartments, the sampling covered the entire food chain (phyto- and zooplankton, macroalgae, aquatic plants, crustaceans, mollusks, and fish). Of the organisms present, the filter feeder Dreissena polymorpha, the detritivorous Bithynia tentaculata and Orconectes limosus were most contaminated by copper. The level of copper found in fish was the lowest. Body copper concentrations recorded in the present study show large variability between species even in some that are closely related. In most cases, however, the metal handling strategy, feeding habits, morphology and ecology can, at least partially, explain the metal content recorded. Pollution factors have been used to assess the state of contamination of the food chain. This study showed finally that the copper in the lake is bioavailable and bioaccumulated by organisms up to high levels and some effects of long-term toxicity of copper on benthic community and planktonic biomass were pointed out.     

Environmental impact of two successive chemical treatments in a small shallow eutrophied lake: Part II. Case of copper sulfate

The appearance of cyanobacteria ( > 10 colony per ml) was not prevented after alum treatment. In order to prevent cyanobacteria efflorescences in a small shallow polymictic lake (Courtille, France), copper sulfate was applied. Treatment level was 63 microg 1(-1) as Cu2+ from CUSO4, 5 H2O. Cyanobacteria were kept under control during the summer. Microcystis sp. completely disappeared, which allowed swimming in the lake throughout the tourist season. Microcystis only reappeared 2 months after the treatment. Copper content in the water column only returned to its background level 2 months after copper addition. This high residence time of copper in the water might have been caused by complexation and adsorption of copper on natural organic matter, whose level was high in the ecosystem studied. A mechanism of transfer of 'truly' dissolved copper towards particulate copper has been underlined and explains the disappearance of this fraction of copper in the water column.