Sodium silicate as alternative to liming-reduced aluminium toxicity for Atlantic salmon (Salmo salar L.) in unstable mixing zones

When acid aluminium (Al) rich water is limed, unstable mixing zones are formed until equilibrium is reached. in such mixing zones transient high molecular mass positively charged M-species (HMM Al-i) being extremely gill reactive are produced, causing toxic effects in fish. The transient HAW Al-i-species are formed due to hydrolysis and polymerization of low molecular positively charged Al-species (LMM Ali), e.g. initiated by liming and the subsequent increase in pH. To counteract the toxicity of transient Al polymers in such mixing zones, sodium silicate, forming non-toxic hydroxyaluminosilicate (HAS) complexes, can be used as alternative to liming. In the present work the effect of sodium silicate on polymerization of LMM Ali in unstable mixing zones and subsequent gill reactivity and mortality of fish was compared to results obtained from liming. Diluted sodium silicate (