Lead and freshwater fishes: Part 1—Lead accumulation and water pH

Accumulation of lead (Pb) in brown trout (Salmo trutta) from a lake downstream a former shooting range

An environmental survey was performed in Lake Kyrtjønn, a small lake within an abandoned shooting range in the south of Norway. In Lake Kyrtjønn the total water concentrations of Pb (14µg/L), Cu (6.1µg/L) and Sb (1.3µg/L) were elevated compared to the nearby reference Lake Stitjønn, where the total concentrations of Pb, Cu and Sb were 0.76, 1.8 and 0.12µg/L, respectively. Brown trout (Salmo trutta) from Lake Kyrtjønn had very high levels of Pb in bone (104mg/kg w.w.), kidney (161mg/kg w.w.) and the gills (137mg/kg d.w), and a strong inhibition of the ALA-D enzyme activity were observed in the blood (24% of control). Dry fertilized brown trout eggs were placed in the small outlet streams from Lake Kyrtjønn and the reference lake for 6 months, and the concentrations of Pb and Cu in eggs from the Lake Kyrtjønn stream were significantly higher than in eggs from the reference. More than 90% of Pb accumulated in the egg shell, whereas more than 80% of the Cu and Zn accumulated in the egg interior. Pb in the lake sediments was elevated in the upper 2-5cm layer (410-2700mg/kg d.w), and was predominantly associated with redox sensitive fractions (e.g., organic materials, hydroxides) indicating low potential mobility and bioavailability of the deposited Pb. Only minor amounts of Cu and Sb were deposited in the sediments. The present work showed that the adult brown trout, as well as fertilized eggs and alevins, may be subjected to increased stress due to chronic exposure to Pb, whereas exposure to Cu, Zn and Sb were of less importance.

Lead induced malformations in embryos of the African catfish Clarias gariepinus (Burchell, 1822)

The effect of lead exposure (100, 300, and 500 microg/L lead nitrate) on embryos of the African catfish Clarias gariepinus were examined by gross morphology and histopathology. Exposition to lead nitrate caused a progressively longer delay in hatching and also reduced the percentage of embryos, which successfully completely hatch from 75% in the control group to 40% in the group exposed to 500 microg/L lead. Categories of gross morphological abnormalities comprised four major ones (irregular head shape, pericardial edema, yolk sac edema, and notochordal defect) and two minor deformations (finfold defect and reduction of pigmentation). The frequencies of recorded morphological malformations increased significantly (P < 0.05) with increasing lead concentration in all stages. Four histopathological categories comprising notochordal defect, gill malformation, eye malformation, and detached skin were recorded. All these malformations were recorded only in the embryos exposed to 300 and 500 microg/L lead. The degrees of histological lesions increased with increasing lead concentration and with length of exposure time. Mean concentrations of lead in the whole embryos were measured and the lowest concentrations of lead were recorded in the control groups (0.3-1.0 microg/g wet wt). Accumulated lead increased significantly (P < 0.05) with increasing dose in all stages. Accumulation of lead in the chorion suggests that the chorion acts as an effective barrier protecting the embryo. Low impact of lead on prehatching stages may be related to both the protective capacity of the chorion and the ability of the perivitelline fluid to concentrate lead. The present results show that (i) lead toxicity was dosage dependent and become evident in gross morphological malformations, followed by histopathological changes, and (ii) early life stages of the African catfish C. gariepinus are a very sensitive bioassay for aquatic lead pollution.

Origin of cadmium and lead in clear softwater lakes of high-altitude and high-latitude, and their bioavailability and toxicity to fish

As a consequence of atmospheric deposition, effects of pollutants such as acidification and metal contamination are evident even in remote aquatic ecosystems of mountain and polar regions. Due to similar environmental characteristics (e.g., oligotrophy, low buffering capacity, long ice-cover, high precipitation rates), clearwater high altitude and high latitude lakes represent very sensitive ecosystems, which are extremely susceptible to even slight changes of the environment. Thus, the environmental relevance of Cd and Pb for both types of lakes is discussed in relation to their extraordinary sensitivity to environmental changes. The impact of Cd and Pb on fish from high altitude and high latitude lakes is reviewed and biotic and abiotic factors controlling bioavailability and toxicity of metals to fish are summarized. Apart from direct toxic effects of low pH, acidification increases the bioavailability of metals for fish. Furthermore, low concentrations of dissolved organic carbon and suspended particles take influence on the uptake and toxicity of metals in fish from clear high altitude and high latitude lakes. Since even very low concentrations of Cd and Pb may result in high metal concentrations in fish, evaluation of critical metal loads for clear high altitude and high latitude lakes is of major importance.

Metal bioavailability and toxicity to fish in low-alkalinity lakes: A critical review

Fish in low-alkalinity lakes having pH of 6.0-6.5 or less often have higher body or tissue burdens of mercury, cadmium, and lead than do fish in nearby lakes with higher pH. The greater bioaccumulation of these metals in such waters seems to result partly from the greater aqueous abundances of biologically available forms (CH(3) Hg(+), Cd(2+), and Pb(2+)) at low pH. In addition, the low concentrations of aqueous calcium in low-alkalinity lakes increase the permeability of biological membranes to these metals, which in fish may cause greater uptake from both water and food. Fish exposed to aqueous inorganic aluminum in the laboratory and field accumulate the metal in and on the epithelial cells of the gills; however, there is little accumulation of aluminum in the blood or internal organs. In low-pH water, both sublethal and lethal toxicity of aluminum has been clearly demonstrated in both laboratory and field studies at environmental concentrations. In contrast, recently measured aqueous concentrations of total mercury, methylmercury, cadmium, and lead in low-alkalinity lakes are much lower than the aqueous concentrations known to cause acute or chronic toxicity in fish, although the vast majority of toxicological research has involved waters with much higher ionic strength than that in low-alkalinity lakes. Additional work with fish is needed to better assess (1) the toxicity of aqueous metals in low-alkalinity waters, and (2) the toxicological significance of dietary methylmercury and cadmium.

Mercuric chloride stress on serum transaminase activity in Notopterus notopterus

Mercuric intoxication at sublethal levels (1/5, 1/10, 1/15, 1/20 or 1/25 fractions of 96 h LC50) produced alterations in the activity of serum glutamic oxalacetic transaminase (SGOT) and serum glutamic pyruvic transaminase (SGPT) of Notopterus notopterus. The difference between control and treated fish was found to be significant at P less than 0.05, P less than 0.01 and P less than 0.001 levels. Maximum (81.75%) significant (P less than 0.001) effect was observed in SGOT: maximum (69.23%) significant (P less than 0.001) effect was observed in SGPT in fish exposed for 60 days.