Studies on the toxicity of copper sulphate to stone loach Noemacheilus barbatulus (L.) in hard water

The toxicity of copper sulphate to Noemacheilus barbatulus was studied for 64 days in a water of total hardness 249 mg l⁻¹ as CaCO₃. The 63-day lc₅₀ was approximately 0.25 mg Cu l⁻¹. Larger fish survived longer, and at concentrations greater than 0.29 mg l⁻¹ fish hid less during daylight. Noemacheilus surviving 0.12 mg Cu l⁻¹ for 64 days shed copper when placed in clean water for 7 days: gill, muscle, eye and vertebrae lost significant amounts of copper during this period. The opportunity to shed copper during a short period when the poison supply to their tank failed, may have allowed fish exposed to 0.49 mg l⁻¹ to live 12 days longer than expected. The sensitivity of Noemacheilus to copper, cadmium and zinc was compared with that of rainbow trout. Salmo gairdneri.     

Speciation and rate of loss of copper from lakewater with implications to toxicity

The rates of disappearance of total dissolved copper in six prairie “pothole” hard water lakes treated with copper were measured. The first-order rate constants ranged from 1.01 to 0.11 day⁻¹, and the half-times from 1 to 7 days. Concentrations of 12 inorganic copper species and the humic acid-copper complex were calculated for the pH range of each lake. Less than 0.5% of total dissolved copper was calculated to be present at any time as free cupric ion. The total dissolved concentration of added copper was reduced with time probably through precipitation of tenorite (in some cases malachite) and by adsorption on solids.The effectiveness of copper as an algicide in these lakes at the relatively low concentration of added copper is explained in terms of a “total toxic copper” concept, which includes the species Cu(OH)₂⁰ and CuOH⁺ in addition to cupric ion, the generally recognized toxic species.     

The stabilization of “dissolved” iron in freshwaters

Laboratory experiments have been conducted to see what substances are capable of holding iron at a concentration of about 1 ppm in a “dissolved” form (i.e. will pass through a 0.45 μm pore size filter) in oxygenated water. The results show that reagents capable of doing this include humic and tannic acids, surfactants such as sodium dodecyl sulphate and sodium dodecylbenzene sulphonate, and the inorganic ions silicate and phosphate. In contrast, the synthetic polymer polyvinylpyrrollidone and the simple ions Cl⁻, HCO₃⁻, SO₄⁻ and NO₃⁻ showed no ability to stabilise iron. The efficiency of phosphate at keeping iron in the “dissolved” state was found to decrease in the presence of cations, particularly divalent ones, but increased with rise in water pH in the range 6–11.It seems unlikely that much of the stabilization observed for any of the reagents tested is due to their forming complexes with the iron. A much more likely explanation is that the substances for which positive results were obtained are able to stabilize fine colloidal iron particles and inhibit them from forming larger aggregates.     

Detoxification of seawater used for gas scrubbing in the steel industry

Cyanide ion present in seawater after scrubbing blast furnace and coke ovens gases can be removed by sedimentation of hexacyanoferrate complexes followed by oxidation of residual cyanide with Caro's acid. Zinc ion is removed at the same time by adsorption on the hexacyanoferrate/hydrous ferric oxide precipitate.Sulphide is precipitated as ferrous sulphide, then oxidised by atmospheric oxygen. At 25°C and using an Fe/CN ratio of 1·00, initial concentrations of 50 mg l⁻¹ of CN⁻ and 10 mg l⁻¹ of Zn²⁺ in seawater are reduced to 5–7 mg l⁻¹ and 0·1 mg l⁻¹. Subsequent treatment with H₂SO₅/CN = 1·2 reduces the [CN⁻] to 0·1 mg l⁻¹.Treatment of a combined blast furnace/coke ovens effluent ([CN⁻] = 24 mgl⁻¹, [Zn²⁺] = 4·0 mgl⁻¹) with Fe/CN = 1·5 reduced [CN⁻] to 0·2 mg l⁻¹ and [Zn²⁺] to <0·1 mgl⁻¹. Subsequent treatment with H₂SO₅/CN = 2·0 reduced [CN⁻] to 0·2 mg l⁻¹. The process operates best in the pH range 7–9 and so is not affected by the buffer characteristics of seawater.     

Conditions required for the precipitation of aluminium in acidic natural waters

Laboratory and field studies were carried out in order to define the conditions necessary for the precipitation of Al in natural waters of pH 4–6. It is concluded that if precipitation does occur it involves the formation of Al(oxy)hydroxide, not aluminosilicates or basic aluminium sulphates. The solubility product of the Al(oxy)hydroxide is highly temperature dependent (ΔH = −30.5 kcal⁻¹). It is also sensitive to concentrations of SO₄²⁻ and, more markedly, humic substances (HS); both of these decrease solubility, HS by more than an order of magnitude at a concentration of approx. 5 mg l⁻¹ (equivalent to approx. 2.5 mg l⁻¹ dissolved organic carbon). A semi-empirical equation is proposed that allows the prediction of the effective solubility product at different temperatures and at humic concentrations in the range 0–7 mg l⁻¹. Of the 113 natural water samples analysed, only one was calculated to be oversaturated with respect to Al(oxy)hydroxide.     

The toxic effect of copper on algae and rotifers from a Soda Lake (Lake Nakuru, East Africa)

The effect of Cu(II) ions on the photosynthetic oxygen production of the phytoplankton, the growth rate of the blue-green algae Spirulina platensis and the population of rotifers (Brachionus sp.) in water from the soda lake Nakuru in Kenya was investigated experimentally. The photosynthetic production was reduced to 80% of the control by the addition of 0.1 mg Cu l⁻¹ and 50% by addition of 0.15–0.20 mg Cu l⁻¹. The growth rate of Spirulina platensis was more affected by copper than the photosynthesis of phytoplankton. Addition of 0.05 mg Cu l⁻¹ reduced the growth rate to about 40% of the control. The rotifiers were less sensitive to copper than the algae, but after 8 days exposure to 0.5 mg Cu l⁻¹ or more the population was severely affected.     

Oxidative removal of aqueous steroid estrogens by manganese oxides

This study investigated the oxidative removal of steroid estrogens from water by synthetic manganese oxide (MnO₂) and the factors influencing the reactions. Using 1 × 10⁻⁵ M MnO₂ at pH 4, estrone (E1), 17β-estradiol (E2), estriol (E3) and 17α-ethinylestradiol (EE2), all at 4 × 10⁻⁶ M, were rapidly removed within 220 min, indicating the effectiveness of MnO₂ as an oxidizing agent towards estrogens. E2 removal increased with decreasing pH over the tested range of 4-8, due most likely to increased oxidizing power of MnO₂ and a cleaner reactive surface in acidic solutions. Coexisting metal ions of 0.01 M (Cu(II), Zn(II), Fe(III) and Mn(II)) and Mn(II) released from MnO₂ reduction competed with E2 for reactive sites leading to reduced E2 removal. Observed differential suppression on E2 removal may be related to different speciations of metals, as suggested by the MINTEQ calculations, and hence their different adsorptivities on MnO₂. By suppressing the metal effect, humic acid substantially enhanced E2 removal. This was attributed to complexation of humic acid with metal ions. With 0.01 M ZnCl₂ in solutions containing 1 mg l⁻¹ humic acid, the binding of humic acid for Zn(II) was determined at 251 mmol g⁻¹. An in vitro assay using human breast carcinoma MCF-7 cells indicated a near elimination of estrogenic activities without secondary risk of estrogen solutions treated with MnO₂. Synthetic MnO₂ is therefore a promising chemical agent under optimized conditions for estrogen removal from water. Metal chelators recalcitrant to MnO₂ oxidation may be properly used to further enhance the MnO₂ performance.     

Copper lethality to rainbow trout in waters of various hardness and pH

The 96 h median lethal concentration (LC₅₀) of total dissolved copper varied from 20 μg 1⁻¹ in soft acid water to 520 μg l⁻¹ in hard alkaline water, in tests with hardness ranging from 30 to 360 mg l⁻¹ as CaCO₃ and pH from 5 to 9. The 3-dimensional response surface was complex, although an increase in hardness usually made copper less toxic. A good prediction of copper LC₅₀ at usual combinations of hardness and pH was given by the equation: LC₅₀ = antilog (1.933 + 0.0592 P_T + 0.4912 H_T + 0.4035 P_TH_T + 0.4813 P²_T + 0.1403 H²_TThe transformed variables are and A somewhat less accurate equation is provided for extreme combinations of hardness and pH.Trout of 10 g weight were 2.5 times more resistant than 0.7 g trout. Effect of size was apparently the same at different combinations of hardness and pH, and was predictable by an equation of the form LC₅₀ = Constant × Weight ^0.348.Ionic copper (Cu²⁺) and two ionized hydroxides (CuOH⁺ and Cu₂OH²⁺₂) seemed to be the toxic species of copper, since they yielded the smoothest response surface with the best fit to measured LC₅₀'s. The sum of these ions produced LC₅₀'s ranging from 0.09 μg l⁻¹ copper in soft alkaline water to 230 μg l⁻¹ in hard acid water. The ions were different in relative toxicity, or became more toxic at high pH, or both.     

Environmental chemistry of copper in Lake Monona, Wisconsin

Lake Monona, located at Madison, Wisconsin, received over 1.5 × 10⁶ pounds of copper sulfate in the past 50 yr to control excessive algal growth. Dissolved copper on Lake Monona epilimnion is inversely related to pH which indicates possible control of dissolved copper by basic copper carbonate. Concentrations as high as about 4 μg Cu l⁻¹ were found in Lake Monona epilimnion, which also contains 3.3 me l⁻¹ (milliequivalents per liter) of alkalinity, mostly bicarbonate. Concentrations of dissolved copper were consistently lower (0.3 μg Cu l⁻¹) in the hypolimnion. Sulfide probably controls dissolved copper in the hypolimnion during anoxic conditions because of sulfide insolubility. Particulate copper concentrations of about 3 μg l⁻¹ increased slightly with depth. The highest concentrations of copper in Lake Monona sediments (650 mg kg⁻¹) were found approximately 60 cm below the current sediment surface. Surface sediments of Lake Monona contained approximately 250 mg Cu kg⁻¹ sediment dry weight.     

Complexation and toxicity of copper and the free metal bioassay technique

The concentrations of free and total copper toxic to Daphnia and guppies were determined in inorganic media with and without addition of various concentrations of β-alanine, glycine, glutamic acid or Tris. Free copper concentrations were determined using a cupric ion electrode. Stability constants calculated for each of the detected complexes compared favourably with previously published values, with the possible exception of the Cu(OH)₂ complex. Free copper concentrations in solutions equally toxic to Daphnia were observed to vary greatly, primarily because of the toxicity of copper amino acid complexes to this organism. The copper/amino acid complexes were, nevertheless, less toxic than the free copper ions. The copper/β-alanine complex was observed to be less toxic to guppies than to Daphnia, indicating a difference in sensitivity to different copper complexes in different organisms. Copper/Tris complexes were found to be only slightly toxic to both Daphnia and guppies. A bioassay technique for determining free copper concentrations by comparing copper toxicity before and after addition of Tris was tested and verified. Although free metal concentrations can be determined from properly conducted bioassays, the variation in free metal concentration in equally toxic solutions demonstrates that free metal concentrations cannot be calculated by simply comparing metal toxicity in a test solution with toxicity of the same metal in a standard solution with known free metal concentration, unless it is known that no complexes are present in the test solution which can form toxic complexes with the metal.     

Recovery of chromium(VI) from wastewaters with iron(III) hydroxide—I: Adsorption mechanism of chromium(VI) on iron(III) hydroxide

Chromium(VI) [Cr(VI)] is adsorbed as HCrO⁻₄ on iron(III) hydroxide at pH below 8.5. The Cr(VI) adsorption is suppressed by the presence of other anions such as SO²⁻₄ and SCN⁻, and enhanced by the presence of metal ions such as Cd(II) and Pb(II). The suppression is due to the competitive adsorption of other anions, depending upon the stability of their iron complexes. The enhancement is probably due to the increase in adsorption sites as a result of coprecipitation of metal ion with iron(III) hydroxide.     

Anodic stripping voltammetric study of the lability of Cd, Pb, Cu ions sorbed on humic acid particles

The sorption of Cd, Pb and Cu by humic acid particles has been studied at μg l⁻¹ levels using A.S.V. on a Hg film electrode as the measuring technique. The variables examined included amount of solid present (0.01–0.2% w/v), initial metal ion concn (10–100 μg l⁻¹), systems pH (5.3, 6.35, 8.15) and base electrolyte composition. The calculated capacity for specific adsorption of the metal ions was a few mmol M²⁺ kg⁻¹, or less. The apparent lability of part of the sorbed material was examined by analysing the base solution before and after filtering, and by adding Chelex 100 particles to the suspension. Some sorbed Cd²⁺ was A.S.V. labile, another fraction transferred to the resin. The effect of solution reactions on uptake was studied by making the 1 M CH₃COONa base solution 0.2 M in a range of Na⁺ salts (8 different anions), or in carboxylic acid content (5 acids) or in compounds having S-type bonding groups. Formation of complex ions in solution altered the extent of metal ion uptake, and in the case of Cu A.S.V. peak size, shape and position were varied. It is suggested that natural waters containing suspended matter should be analysed by A.S.V. “as received”, as well as after filtration since response differences provide guidance in respect to the lability of sorbed ions.     

Effect of copper on nitrification in activated sludge

The concentration of free copper in activated sludge with copper added is strongly influenced by pH. For example, at pH 6.5 with 9.13 × 10⁻⁵ mol Cu l⁻¹, the free copper concentration is 4.0 × 10⁻⁷ mol l⁻¹ (pCu = 6.4) and at pH 8.4 this concentration is 10⁻⁸ mol l⁻¹ (pCu = 8.0). In both cases the activated sludge concentration is 0.7 g MLSS l⁻¹. The free copper concentration is also affected by the concentration of mixed liquor suspended solids (MLSS).In batch experiments with constant pH, the effect of copper on the nitrification rate was not regulated by total copper concentration but by copper/sludge ratio or by free copper concentrations. Experiments at different pH showed a linear correlation between nitrification capacity and free copper concentration, suggesting that the pH effect on nitrification below 8.3 is in fact a copper effect.Activated sludge with copper did not become acclimatized to the copper in a period of three days. Addition of nitrilotriacetic acid (NTA) within one day did cancel the copper inhibition.The results were compared with the effect of copper on acetate removal by heterotrophic micro-organisms. The nitrifiers proved to be no more susceptible to copper than heterotrophic micro-organisms.     

The methanogenic toxicity and anaerobic degradability of a hydrolyzable tannin

Gallotannic acid was found to be highly toxic to methanogenic activity. Concentrations, representing 50% inhibition, approximated 700 mg l⁻¹. The toxicity was persistent despite the rapid degradation of gallotannic acid to volatile fatty acids and methane. A 72.5% loss of sludge activity was associated with a 1 day exposure of methanogenic granular sludge to 1000 mg l⁻¹ gallotannic acid. The toxicity of gallotannic acid was persistent over 2 month assay periods. The monomeric derivatives of gallotannic acid, gallic acid and pyrogallol were much less toxic. The 50% inhibition concentration of the monomers approximated 3000 mg l⁻¹ and their toxicities were not persistent. No activity losses were evident after sludge was exposed to 3000 mg l⁻¹ gallic acid for 19 days.The lower toxicities of the monomers compared to the gallotannic acid polymer suggests that the mechanism of toxicity was “tanning”, since data in the literature indicate that tannin polymers are more effectively adsorbed and precipitated with proteins compared to their monomeric counterparts. Functional proteins (enzymes) located at accessible sites in or on the methane bacteria are most likely disturbed by the tanning action.     

Effects of inorganic complexing on the toxicity of copper to Daphnia magna

Effects of carbonate-bicarbonate, orthophosphate, and pyrophosphate on the toxicity of copper (II) to Daphnia magna were studied at constant pH and total hardness. Mortality rates and reciprocal survival times were directly correlated with cupric (Cu²⁺) and copper hydroxy (Cu(OH)n) ion activities as determined by equilibrium calculations. Toxicity was negatively related to activities of soluble copper carbonate (CuCO₃) and other complexes, and was found to be independent of dissolved copper or total copper concentrations.     

Adsorption characteristics of some Cu(II) complexes on aluminosilicates

The adsorption of Cu(II) by aluminosilicates with varying Si/Al ratios was investigated. The presence of complex-forming organic ligands [nitrilotriacetate (NTA) and glycine (Gly)] alters metal electrovalency and, in so doing, modifies Cu(II) adsorption characteristics which can influence its fate, biological activity and transport in aquatic systems. Electrostatic attraction by a positively-charged aluminosilicate surface is an important mechanism whereby anion CuNTA⁻ complexes were adsorbed. Two distinct mechanisms are involved in the adsorption of cationic complexes: (1) an exchange reaction at permanent structural sites and (2) interfacial accumulation in response to the pH-dependent surface charge. The contribution of each mechanism to the total amount of CuGly⁺ adsorbed is related to the Si/A1 ratio. At the critical Si/A1 ratio (Si/A1_iso), the aluminosilicates have zero net pH-dependent surface charge. In the absence of specific adsorption, aluminosilicates for which Si/A1 ≥ Si/A1_iso can only function as cation exchangers. For Si/A1 < Si/A1_iso simultaneous adsorption of anions and cations is possible.     

Nitrate determination in fresh and some estuarine waters by ultraviolet light absorption: A new proposed method

The new proposed u.v./resin technique for nitrate determination is either not affected by, or can allow for, the following interfering chemicals at levels occurring in natural polluted or unpolluted waters; chloride, phosphate, sulphate, carbonate/bicarbonate, bromide, nitrite, coloured metal complexes, humic acids, ammonium, dyes, detergents, phenol and other u.v. absorbing organics. The method is quick and has an accuracy of ±3%. Concentrations of NO₃.N in the range 0.1–3.0 mg l⁻¹ can be determined in fresh water. Concentration of the sample to determine lower levels by evaporation is feasible with certain upland waters but should not be attempted if the sample has a high humic acid concentration. The technique can only be used in nitrate rich estuarine and coastal waters because the lower limit of detection is raised to 0.5 mg l⁻¹ when the sample is diluted to remove bromide interference.     

Removal of heavy metals from electroplating rinsewaters by precipitation, flocculation and ultrafiltration

Chromium, nickel, copper and zinc can be effectively removed from electroplating rinsewaters by hydroxide precipitation, flocculation and ultrafiltration. Prior to precipitation, chromium is reduced from the hexavalent to the trivalent form by ferrous sulfate and cyanide in copper and zinc rinsewaters are oxidized by sodium hypochlorite. Minimum metal concentrations in the permeate from separate batches of chromium, nickel, copper and zinc rinsewaters were found to be, respectively, 0.17 mg 1⁻¹ Cr (T), 0.26 mg 1⁻¹ Ni, 0.30 mg 1⁻¹ Cu and 1.84 mg 1⁻¹ Zn. These solubilities are in good agreement with the theoretical solubility curves, except for copper where the formation of stable copper cyanide complexes appears to increase the solubilities at least two orders of magnitude relative to those predicted on the basis of the equilibrium constants for copper hydroxides and oxides. A simple mass balance model, assuming concentrate recycle and constant metal concentration in the permeate, is adequate for the prediction of feed and permeate concentrations as a function of the volume filtered up to a relative volume of about 0.3. Above this value, the feed concentrations are lower than predicted, apparently because of entrapment of metal precipitate in the strainer. Water recoveries are strongly dependent on the specific metal removed and are found to be 24% for Ni with a 0.20 μm membrane, 10% for Cr with a 0.80 μm membrane, 6.5% for Cu and 3.7% for Zn, both with a 0.45 μm membrane.     

Aluminium complexation by an aquatic humic fraction under acidic conditions

Equilibrium dialysis and acid-base titration were used to investigate the interactions between Al and a fraction of aquatic humic substances (HS), in the pH range 3–5. Binding of Al by the HS increased with Al³⁺ activity and with pH. Under conditions relevant to natural waters, υ (mol Al bound per gHS) varied from 0 to 1.5 × 10⁻³. The data were modelled with an emprical linear logarithmic expression (Model I) and on the basis of the polyelectrolyte nature of the HS, incorporating competitive binding of H⁺ and Al³⁺ (Model II). Both models gave tolerable fits (r = 0.93). Model I is simpler to apply, while Model II allows the calculation of proton release accompanying Al binding, and provides information on the net charge of the Al---HS complexes. The results were used to calculate the distribution of Al between organic and inorganic forms under conditions prevailing in acidic natural waters.     

Bioaccumulation and toxicity of copper as affected by interactions between humic acid and water hardness

This study evaluated the effects of water hardness and humic acid (HA) on the acute and chronic toxicity of copper to Daphnia pulex and on its accumulation by D. magna. Hardness had little effect on either the acute (3-day) or the chronic (42-day) toxicity of copper. Humic acid significantly reduced both the acute and chronic toxicity of copper when added to waters having hardnesses of 58, 115 and 230 mg l^?1 as CaCO₃. The effect, per unit of HA, on chronic toxicity was very similar for soft and medium water but less in hard water. At each of two HA concentrations, copper was chronically more toxic in hard water than in either medium or soft water. Bioaccumulation of copper varied with relative hardness and HA concentration and this was further affected by age at exposure. For 1-day-old animals, an increase in either hardness or HA- or any combination of the two, tended to decrease bioaccumulation. Results for 7-day-old animals were in general agreement except for animals exposed to copper in hard water at an intermediate HA concentration. These animals accumulated significantly more copper in the presence of HA. This agrees with the fact that this concentration of HA also increased the chronic toxicity of copper in hard water. Both of those phenomena are probably due to the displacement of Cu²⁺ from HA by competition from the increased concentrations of Ca²⁺ and Mg²⁺. The fact that HA had the opposite effect on copper accumulation by young animals in hard water could not be explained.