Abstract
Metals are present in aquatic environments as a result of natural and anthropogenic inputs, and may induce toxicity to organisms. One of the main factors that influence this toxicity in fresh water is natural organic matter (NOM) but all NOMs are not the same in this regard. In sea water, possible protection by marine NOMs is not well understood. Thus, our study isolated marine NOMs by solid-phase extraction from five different sites and characterized them by excitation-emission fluorescence analysis—one inshore (terrigenous origin), two offshore (autochthonous origin), and two intermediate in composition (indicative of a mixed origin). The physiological effects of these five NOMS alone (at 8 mg/L), of three metals alone (copper, lead and zinc at 6 µg Cu/L, 20 µg Pb/L, and 25 µg Zn/L respectively), and of each metal in combination with each NOM, were evaluated in 48-h exposures of mussel larvae. Endpoints were whole body Ca2++Mg2+-ATPase activity, carbonic anhydrase activity and lipid peroxidation. By themselves, NOMs increased lipid peroxidation, Ca2++Mg2+-ATPase, and/or carbonic anhydrase activities (significant in seven of 15 NOM-endpoint combinations), whereas metals by themselves did not affect the first two endpoints, but Cu and Pb increased carbonic anhydrase activities. In combination, the effects of NOMs predominated, with the metal exerting no additional effect in 33 out of 45 combinations. While NOM effects varied amongst different isolates, there was no clear pattern with respect to optical or chemical properties. When NOMs were treated as a single source by data averaging, NOM had no effect on Ca2++Mg2+-ATPase activity but markedly stimulated carbonic anhydrase activity and lipid peroxidation, and there were no additional effects of any metal. Our results indicate that marine NOMs may have direct effects on this model marine organism, as well as protective effects against metal toxicity, and the quality of marine NOMs may be an important factor in these actions.
Highlights
Metals are naturally present in the aquatic environment; depending on their concentration, availability and residence time they have the potential to cause animal toxicity, especially in pollution-impacted environments (Wood, 2012)
Our specific hypotheses were: (i) that at least some of the natural organic matter (NOM) would exert positive effects on the organism; (ii) that metals alone would exert negative effects, which would differ according to the metal; (iii) that at least some of the NOMs would be protective, ameliorating the negative effects of the metals; and (iv) that these effects would vary both amongst the different NOMs, and among the different metals
Similar classifications of the sources resulted from looking at the fluorescence index (FI) which was higher for more authochthonous sources and lower for terrigenous sources (Table 1)
Summary
Metals are naturally present in the aquatic environment; depending on their concentration, availability and residence time they have the potential to cause animal toxicity, especially in pollution-impacted environments (Wood, 2012). Zinc (Zn, reviewed by Hogstrand, 2012) and lead (Pb, reviewed by Mager, 2012) cause ionoregulatory dysfunction but mainly for calcium (Ca2+) homeostasis because calcium transport sites (apical Ca2+ channels and basolateral Ca2+-ATPase) are impacted by these metals. These may not be the only mechanisms of toxicity, and there is emerging evidence that metals may induce oxidative stress (Lushchak, 2011) and inhibit a key gill enzyme, carbonic anhydrase (Wood, 2012; Zimmer et al, 2012)
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