TOC levels (Fig. 3A) are substantially higher and more variable in Norwegian than in Chilean water. Given the nature of water sources, this is to be expected. Fulvic acids in TOC of humic origin contribute to low pH in Norway (Lydersen et al., 2002), and also contribute to transport of associated metals. Metals bound to humic substances are generally less bioavailable than low molecular weight metal species (also denoted free metal ions) and elevated TOC may thus serve to protect fish from harmful effects of metals provided remobilization is not enhanced by decreased pH (Andre´n et al., 2006; Rosseland and Staurnes, 1994),