J.L. Stauber

Toxicity of copper complexes to the marine diatom Nitzschia closterium

Abstract Copper ions initially bind to Nitzschia with a stability constant, β1, in the range logβ1 10, a value which precludes sulfur bonding and suggests involvement of a membrane protein. Although the algal growth rate in sea water was halved by 20 μg Cu·1−1, photosynthesis was not affected until the copper concentration was above 100 μg Cu·1−1. This decoupling of growth and photosynthesis did not occur to the same extent with other algae species tested, and it is proposed that it results from an intracellular reaction between Cu2+ and GSH, leading to a lowering of the GSH/GSSG ratio and suppression of mitosis. Water-soluble ligands generally decreased the toxicity of copper, whereas lipid-soluble copper complexes were highly toxic. Oxine, 2,9-dimethyl-1,10-phenanthroline, and pyridyl- and thiazolyl-hydroxyazo compounds formed exceptionally toxic complexes. The toxicity of many redox-active compounds and their copper complexes appears to be due, at least partly, to the intracellular generation of hydrogen peroxide during oxidation of these compounds, an effect exacerbated by the ability of copper to inhibit catalase. Hydrogen peroxide is highly toxic towards marine algae, and may be a natural growth-inhibiting factor. Hydroxyl radicals (OH·), generated intracellularly from a mixture of hydrogen peroxide and the lipid-soluble thiol, cysteine, were also extremely toxic. However, when OH· or superoxide radicals O2sce; were generated extracellularly, no effect on growht rate was observed, even though singlet oxygen (1O2) did seriously reduce growth.

Occurrence and a screening-level risk assessment of human pharmaceuticals in the Pearl River system, South China.

Ten nonsteroidal antiinflammatory drugs (NSAIDs), two blood lipid regulators (BLRs), and two antiepileptic drugs (AEDs) were analyzed in the Pearl River system in China (i.e., Liuxi, Zhujiang, and Shijing Rivers) and four sewage effluents during the dry and wet seasons, and the environmental risks they posed were assessed. Eight pharmaceuticals were detected in the rivers and effluents, including five NSAIDs (salicylic acid, ibuprofen, diclofenac, mefenamic acid, and naproxen), two BLRs (clofibric acid and gemfibrozil), and one AED (carbamazepine). The median concentrations for the eight pharmaceuticals ranged from 11.2 to 102 ng/L. Seasonal variations were not obvious for most pharmaceuticals in the three rivers, except for salicylic acid and clofibric acid in the Zhujiang River, and diclofenac in the Zhujiang and Shijing Rivers. However, spatially considerable variations in the concentrations were observed for the eight pharmaceuticals in all three rivers. For most of the pharmaceuticals, the effluents from the four wastewater treatment plants and Shijing River water were found to be the major discharge sources for the Zhujiang River, but with additional discharge sources from some small urban streams in the wet season. Diclofenac in the Shijing River was the only pharmaceutical that had a risk quotient (RQ) >1, indicating a high risk to aquatic organisms in the river. Although higher RQs were calculated for the mixture of the pharmaceuticals in each river, the risk rating remained the same for the three rivers with the RQ being >1 only in Shijing River.

The effect of culture medium on metal toxicity to the marine diatom Nitzschia closterium and the freshwater green alga Chlorella pyrenoidosa

Abstract The composition of the culture medium and its effects on the toxicity of ionic copper and zinc to the marine diatom Nitszchia closterium and the toxicity of copper and lead to the freshwater green alga Chlorella pyrenoidosa were examined. The inhibitory concentration of copper giving 50% reduction in cell division rate in C. pyrenoidosa increased from 16 μg Cu l−1 in synthetic softwater and 24 μg Cu l−1 in EPA-AAP medium (minus EDTA) to >200 μg Cu l−1 in high nutrient MBL medium. Similarly, marine medium f reduced copper and zinc toxicity to N. closterium 10–20 fold compared to seawater. To overcome the problems of metal complexation by chelators such as silicate, iron and EDTA in the assay medium, unsupplemented seawater and buffered synthetic softwater, enriched only with nitrate and phosphate, have been used for the study of metal toxicities to marine and freshwater algae. These low nutrient media are sufficient to support algal growth over the 4-day assay period.

Percutaneous absorption of inorganic lead compounds

In vivo experiments with the stable lead isotope, 204Pb, have confirmed that inorganic lead compounds can be absorbed through the skin. Three different analytical techniques--thermal ionization mass spectrometry, inductively coupled plasma mass spectrometry and anodic stripping voltammetry--showed that lead, as lead nitrate or lead acetate, was rapidly absorbed through the skin and detectable in sweat, blood and urine within 6 h of skin application. Of the 4.4 mg of lead applied to the skin in one experiment, 1.3 mg was absorbed within 24 h. Initial rapid uptake was probably via sweat glands and hair follicles, followed by slower absorption via the transepidermal route. While increases in 204Pb concentration and abundance were observed, no increase in total lead in blood or urine was found. It is possible that the physicochemical form of skin-absorbed lead partitions strongly into extracellular fluid, but has a low affinity for erythrocytes. There was no significant difference in uptake of lead into erythrocytes (in vitro) from normal saline, synthetic sweat or sauna sweat. Ultrafiltration of sweat showed that up to 70% of lead in sweat was associated with > 30,000 MW particles. It is possible that percutaneous absorption of lead could contribute significantly to lead body burden, particularly from occupational exposure to lead in dust. Moreover, because lead absorbed through the skin was only just detectable in blood, and blood lead is the main criterion by which industry determines exposure, skin-absorbed lead may remain undetected.

Toxicity of lipid-soluble copper(II) complexes to the marine diatom Nitzschia closterium: Amelioration by humic substances

Algal assays, using the marine diatom Nitzschia closterium, have established that humic acid (5 mg kg−1) can ameliorate the toxicity of the lipophilic complex Cu(oxine)2 (3 × 10−8 mol l−1 in unsupplemented seawater). The toxicity of Cu(PAN)2 is not ameliorated [PAN = 1-(2-pyridylazo)-2-napthol]. In conjunction with previous visible absorption spectrophotometry and polarographic measurements it was established that humic acid sequesters copper(II) from the hydrophobic complexes, releasing a ligand molecule. The copper(II) toxicity may be ameliorated provided the ligand itself is not toxic. Fulvic acid was significantly less effective in ameliorating toxicity. Because of the significant competition from Ca(II) and Mg(II) in seawater, it is inferred that humic substances may be more effective in ameliorating toxicity of hydrophobic copper complexes in fresh water.

Revisions to the derivation of the Australian and New Zealand guidelines for toxicants in fresh and marine waters.

The Australian and New Zealand Guidelines for Fresh and Marine Water Quality are a key document in the Australian National Water Quality Management Strategy. These guidelines released in 2000 are currently being reviewed and updated. The revision is being co-ordinated by the Australian Department of Sustainability, Environment, Water, Population and Communities, while technical matters are dealt with by a series of Working Groups. The revision will be evolutionary in nature reflecting the latest scientific developments and a range of stakeholder desires. Key changes will be: increasing the types and sources of data that can be used; working collaboratively with industry to permit the use of commercial-in-confidence data; increasing the minimum data requirements; including a measure of the uncertainty of the trigger value; improving the software used to calculate trigger values; increasing the rigour of site-specific trigger values; improving the method for assessing the reliability of the trigger values; and providing guidance of measures of toxicity and toxicological endpoints that may, in the near future, be appropriate for trigger value derivation. These changes will markedly improve the number and quality of the trigger values that can be derived and will increase end-users’ ability to understand and implement the guidelines in a scientifically rigorous manner.

Interactions of copper and manganese: A mechanism by which manganese alleviates copper toxicity to the marine diatom, Nitzschia closterium (Ehrenberg) W. Smith

Abstract The mechanism by which manganese (4.2 and 42 μg Mn·1 −1 ) ameliorates the toxicity of copper (0–60 μg Cu·1 −1 ) to the marine diatom, Nitzschia closterium (Ehrenberg) W. Smith, was investigated using unsupplemented sea water for growth rate experiments. Speciation of manganese associated with the cellls, intracellular and extracellular manganese and copper concentrations, and competitive binding between copper and manganese were studied using ultrafiltration, anodic stripping voltammetry and radiochemical techniques. Cells cultured before the sea-water assay and in the absence of manganese accumulated high intracellular copper, and their growth rate was more sensitive to copper than cells cultured in the presence of manganese. Manganese associated with the cells was present as manganese (II) and/or (III) hydroxides, rather than as the fully oxidized MnO 2 . It is proposed that manganese (III) hydroxide, like iron (III) hydroxide and cobalt (III) hydroxide, adsorbs copper very effectively on the membrane surface and prevents its penetration into the cell. Competitive interactions between manganese and copper occurred at the cell surface, but copper had no effect on intracellular manganese. Only 4 μg Mn·1 −1 was required to alleviate copper toxicity, compared to 790 μg Fe·1 −1 . In the presence of algae, copper ions had a greater affinity for manganese in sea water than iron at similar concentrations, which may partially account for the relative effectiveness of manganese as a protective agent. In addition, manganese can scavenge the toxic superoxide radical (O 2 − ), catalyzing its dismutation to H 2 O 2 and O 2 . Manganese was unable to reverse copper toxicity, nor did it inhibit the toxicity of lipid-soluble copper complexes, such as copper oxinate, to N. closterium .

The use of sweat to monitor lead absorption through the skin

It is usually assumed that lead can be absorbed through the skin only if it is present as an organolead compound such as tetraethyllead or lead naphthanate. It has been found, however, that finely-powdered lead metal or lead nitrate solution placed on the skin results in rapid absorption of lead, and transport of the metal around the body. The absorbed lead appears in sweat and saliva, but not in blood or urine. The application of 6 mg of lead as 0.5 M lead nitrate to the left arm resulted in an increase in lead concentration in pilocarpine-induced iontophoresis sweat samples taken from the right arm, from an initial value of 15-25 micrograms Pbl-1 to greater than 300 micrograms Pbl-1 after 2 days. Saliva lead increased from 2.5 to 15 micrograms Pbl-1 in the same period. The rate of lead absorption through the skin increases with increased sweating of the skin. Since no measurable increase in blood lead has been found, the lead must be transported in the plasma and rapidly concentrated into the extracellular fluid pool (sweat and saliva), without significant uptake by the erythrocytes, and with a very low transient concentration in the plasma. Workers occupationally exposed to lead have extremely high levels of lead in sweat even though their lead in blood is only moderately elevated. Lead absorbed through the skin may be eliminated via sweat and other extracellular fluids, and hence not be as great a health hazard as ingested lead, but this will need to be proved by further studies.

A comparative study of copper, lead, cadmium and zinc in human sweat and blood

Zinc, cadmium, lead and copper in sweat from 24 male and 39 female volunteers were determined by anodic stripping voltammetry. Sweating was induced on the forearms by pilocarpine iontophoresis. Average values found for zinc, cadmium, lead and copper in sweat from males were 181 (range 25-863), 1.4 (less than 0.5-10), 41 (6-87) and 103 (less than 5-673) micrograms l-1, respectively. Zinc in sweat from females was significantly higher than in sweat from males (331 micrograms l-1, range 87-836 micrograms l-1), while sweat copper and sweat lead in females were lower (29 micrograms Cu l-1, range less than 5-146 micrograms Cu l-1 and 24 micrograms Pb l-1, range less than 5-66 micrograms Pb l-1). Those taking oral contraceptives showed increased sweat copper concentrations (94 micrograms Cu l-1, range less than 5-480 micrograms Cu l-1) and sweat lead concentrations (36 micrograms Pb l-1, range less than 5-70 micrograms Pb l-1). There was no sex-based difference for copper in sauna-induced sweat. Metal concentrations in sweat were compared with ceruloplasmin, alkaline phosphatase, and total and mobile copper and zinc concentrations in serum in males and females.

Manganese catalysis of dopamine oxidation

Manganese catalysis of the oxidation of dopamine by air was studied as part of an investigation of possible manganese intoxication amongst a group of Aborigines living on manganese-rich soil on Groote Eylandt, in the Northern Territory of Australia. Manganese significantly increased the oxidation rate of dopamine, and the manganese complexes with some purines were especially efficient catalysts. An oxidation mechanism, involving a manganese(II)/(III) redox couple and a semiquinone free radical intermediate, is proposed. Stoichiometric hydrogen peroxide was produced by the oxidation, and the oxidation products of dopamine were highly toxic to the marine diatom Nitzschia closterium. Hydrogen peroxide and the superoxide radical did not oxidize dopamine at physiological pH. Some electrophilic compounds, including ascorbic acid, dehydroascorbic acid and thiamine, effectively inhibited dopamine oxidation. The Groote Eylandt Aborigines are likely to be deficient in ascorbic acid (vitamin C) and thiamine (vitamin B1), and these deficiencies, as well as their lifestyle, may predispose them to manganese intoxication.