Antonio B.S. Poléo

Aluminium polymerization — a mechanism of acute toxicity of aqueous aluminium to fish

Abstract In this article a new theory is presented, whereby the process of aluminium polymerization is a mechanism of acute toxicity of aluminium to fish, as opposed to precipitation of solid Al(OH)3 or cellular internalization of Al3+. Between pH 5.0 and 6.0, where toxicity seems most acute, conditions are favourable for Al polymerization. According to the present theory, positively charged Al-hydroxides bind to negatively charged sites of the gill surface which act as polymerization nuclei. Growth of Al polymers on the gill surface and increased mucus secretion cause severe clogging of the interlamellar spaces. This physical surface effect leads to acute hypoxia. The overall mechanism of aqueous Al toxicity is explained in terms of more than one single process, where the most acutely toxic situation for the fish is during the initial phase of Al polymerization.

Toxicity of acid aluminium-rich water to seven freshwater fish species: a comparative laboratory study.

The present study focuses on the relative sensitivity among freshwater fish species to aqueous aluminium. Seven common Scandinavian fish species were exposed to acidic Al-rich water, acidic Al-poor water, and approximately neutral water as a control. The relative sensitivity among the species to an acute aluminium challenge was documented, and was in the following order: Atlantic salmon, Salmo salar, as the most sensitive; then roach, Rutilus rutilus; minnow, Phoxinus phoxinus; perch, Perca fluviatilis; grayling, Thymallus thymallus; brown trout, Salmo trutta; and Arctic char, Salvelinus alpinus. Substantial mortality was observed in all species when exposed to the Al-rich medium. Some mortality was also observed in minnow, roach, and brown trout exposed to the acidic Al-poor medium and the control medium. A high resistance to aluminium was observed in Arctic char, while perch was found to be more sensitive to aluminium than expected and, for the first time, a toxic response to aqueous aluminium in grayling was documented. Through controlled experimental studies, the results confirm that aluminium is an important factor in the toxicity of acidified waters to freshwater fish species.

Aqueous aluminium eliminates Gyrodactylus salaris (Platyhelminthes, Monogenea) infections in Atlantic salmon.

This study focuses on the effect of acidic water and aqueous aluminium on the monogenean ectoparasite Gyrodactylus salaris, infecting Atlantic salmon (Salmo salar) parr. G. salaris-infected salmon were exposed to various combinations of acidity and aluminium concentrations. The most pronounced effect was the elimination of parasites after 4 days when 202 micrograms Al/l was added to the water. The effect of aluminium was concentration dependent, but was relatively independent of pH (5.2, 5.6 and 5.9). At the lowest pH of 5.0 the effect of aluminium was enhanced. Acidic aluminium-poor water had no or minor effects on the G. salaris infections except at pH 5.0 where all parasites were eliminated within 9 days. The G. salaris populations increased exponentially in untreated control water. The results show for the first time that aqueous aluminium can, to a limited extent, have a positive effect on fish health. This study emphasizes that basic knowledge about abiotic environmental factors is of importance in order to understand the population dynamics, range extension and dispersal of ectoparasites such as G. salaris. Finally, our results suggest that aluminium treatment could form an effective disinfection method against ectoparasites in hatcheries and laboratories, as well as complementing the controversial rotenone treatments used against natural populations of G. salaris.

The influences of temperature on aqueous aluminium chemistry.

Temperature affects the solubility of Al(OH)3(s), the solubility product formed, the hydrolysis and molecular weight distribution of aqueous Al species as well as the pH of the solutions. In the present work, identical solutions of inorganic Al (400, 600, and 800 μg Al L−1) were stored for 1 mo at either 2 or 25 °C. In the solutions stored at 25 °C pH varied from 4.83 to 5.07, while in the corresponding solutions stored at 2 °C pH varied from 5.64 to 5.78. In spite of the relatively low pH at 25 °C, significant amounts of high molecular weight Al species were precipitated from the solution and the solubility product (log*Ks) of (Al(OH)3) (s) was low (9.0). Substantial amounts of high molecular weight Al species were also formed at 2 °C, but the majority was present as colloids in the solution. The solubility product (converted from 2 into 25 °C) was 10.2, reflecting a solubility product of an amorphous (Al(OH)3)(s) phase. The different physico-chemical forms of Al present at 2 and 25 °C should have relevance for water/soil chemistry modeling.

The effect of various metals on Gyrodactylus salaris (Platyhelminthes, Monogenea) infections in Atlantic salmon ( Salmo salar )

Atlantic salmon (Salmo salar) parr (age 0+), infected by the ectoparasite Gyrodactylus salaris, were exposed to aqueous aluminium (Al), copper (Cu), zinc (Zn), iron (Fe) and manganese (Mn), at 4 different concentrations. There was a negative correlation between G. salaris infections and metal concentrations in both Zn- and Al-exposed salmon. In the Zn-experiment, all 4 concentrations tested caused a decrease in the G. salaris infections, while in the Al-experiment the G. salaris infection did not decline at the lowest concentration. The number of G. salaris increased continuously during the experiments in all control groups, and in all groups exposed to Cu, Fe and Mn. At the highest concentration, however, copper seemed to impair the growth of G. salaris infection. The results show that aqueous Al and Zn are environmental factors of importance controlling the distribution and abundance of the pathogen G. salaris. Other pollutants might also have an influence on the occurrence of G. salaris. Finally, the results demonstrate that aqueous Al and Zn have a stronger effect on the parasite than on the salmonid host, suggesting that both metals may be used as a pesticide to control ectoparasites such as G. salaris.

The effects of naturally occurring high and low molecular weight inorganic and organic species on the yolk-sack larvae of Atlantic salmon (Salmo salar L.) exposed to acidic aluminium-rich lake water

Yolk-sac larvae of Atlantic salmon (Salmo salar L.) were exposed to water from two acidic, aluminium rich lakes, Nepptjern and Lomstjern. The average pH of the lakes during the experiments were 4.85 and 5.24. The concentrations of total monomeric aluminium (Ala) were high in both lakes, i.e. 640 ± 22 and 451 ± 16 μg Al 1−1, but the total amount of organic carbon (TOC) differed significantly (1.89 ± 0.04 and 11.6 ± 0.1 mg Cl−1). The larvae were also exposed to cation exchanged and hollow-fiber ultrafiltered water from both lakes. Based on the hollow-fiber ultrafiltration, the toxic aluminium species present were as the inorganic, low molecular weight fraction (mol. wt. < 3 000 Da). Within this fraction, the highest mortality rates [LT50=24.6±0.5 h (n = 6)] were observed in the lake water having the highest amounts of the hydrolysis products, i.e. Al3+, Al(OH)2+ and Al(OH)2+. The aluminium-fluorides, AlOHF+, AlF2+, and AlF2+ were also found to be toxic, but less toxic [LT50=49.6±1.1 h (n=4)] than the aluminium hydrolysis products. Removal of high molecular weight species including inorganic and organic Al species, did not affect the toxicity or the mortality rates. No acute toxicity was observed when the larvae were exposed to the cation exchanged eluates. Thus, the organic aluminium-complexes seemed to have no acute toxic effect, at least at the concentration levels tested.

The influence of temperature on aqueous aluminium chemistry and survival of Atlantic salmon (Salmo salar L.) fingerlings

Abstract The present study is mainly focusing on the effect of temperature on Al-chemistry and the resulting toxicity to fish. Atlantic salmon (Salmo salar L.) fingerlings were exposed to water at defined combinations of temperature, pH and Al-concentration, and mortality was recorded. Mortality was correlated to the concentration of inorganic aluminium, and increased systematically with increasing temperature. The degree of ongoing Al-polymerization is thought to be the most important factor for the temperature dependent Al-toxicity observed.

The effect of aluminium in Atlantic salmon (Salmo salar) with special emphasis on alkaline water.

Atlantic salmon (Salmo salar) parr were exposed to aluminium under both steady state and non-steady state chemical conditions in alkaline water. Under alkaline (pH 9.5) steady state conditions, approximately 350 microg Al l(-1) (predominantly aluminate, Al(OH)(4)(-)) had no acute toxic effect on the salmon. The fish, however, showed a physiological response after 3 weeks of exposure ( approximately 300% increase in blood glucose concentration, about 30% increase in blood haematocrit, and about 15% decrease in plasma Cl(-) concentration). No increase in toxicity was evident under non-steady state conditions, i.e. lowering Al solubility as pH was lowered from 9.5 to 7.5. The results indicate that the toxicity of the aluminate ion (Al(OH)(4)(-)) is low, and particularly lower than the corresponding toxicity of cationic Al hydroxides. The effects observed in fish exposed to Al-rich water at pH 9.5 were counteracted as Al solubility was decreased by lowering pH to 7.5. This is contrary to previous observations where Al solubility has been lowered by increasing pH from 5.0 to 6.5.

The effect of aluminium in soft water at low pH and different temperatures on mortality, ventilation frequency and water balance in smoltifying Atlantic salmon, Salmo salar

SynopsisThe present study focuses on the effect of temperature on Al-chemistry and the subsequent toxicity to smoltifying Atlantic salmon, Salmo salar. Fish were exposed to acidic Al-rich water at different temperatures, and mortality, ventilation frequency and various blood parameters were measured. The relationship between temperature and Al-toxicity was documented as mortality increased systematically with increasing temperature. Physiological disturbances at the gills reflected the temperature dependent Al-toxicity. The temperature dependent toxicity observed is probably due to the degree of ongoing Al-polymerization.

Survival of crucian carp,Carassius carassius, exposed to a high low-molecular weight inorganic aluminium challenge

Crucian carp were exposed to three combinations of pH and inorganic aluminium concentrations for 25 days. Mortality, plasma chloride and haematocrit, and gill aluminium content were investigated. No mortality was observed in any of the three exposures. Crucian carp survived acidic Al-rich water (pH 5.17) with a high concentration of low-molecular weight inorganic Al species (242 µgl−1) for 25 days. These fish had lowered plasma chloride levels and high amounts of aluminium on their gills compared to fish exposed to acidic Al-poor water (pH 5.16 and 12 µgl−1 Ali) and control water (pH 6.29 and 4 µgl−1 Ali). Haematocrit was the same in all three exposures. Because aluminium was not acutely toxic to the anoxia tolerant crucian carp, the present results give support to the hypothesis that Al polymerization with subsequent hypoxia is of high importance for the mechanism of acute Al toxicity to fish.