Comparative sensitivity of boreal fishes to UV-B and UV-induced phototoxicity of retene

Abstract

Maapallon elämää suojaava yläilmakehän otsonikerros on ohentunut ihmistoiminnan takia, minkä seurauksena maanpinnalle tulevan UV-B säteilyn määrä on lisääntynyt huomattavasti. Jani Häkkinen arvioi tutkimuksessaan, onko UV-B säteily nykyisillä tai ennustetuilla annostasoilla riskitekijä taloudellisesti ja ekologisesti tärkeimmille makeanveden kalalajeille (siika, muikku ja hauki) niiden herkimmissä kehitysvaiheissa heti kuoriutumisen jälkeen.Häkkinen tutki myös ensimmäistä kertaa pohjoisten alueiden kalalajeilla polyaromaattisten hiilivetyjen (PAH) UV-valossa aktivoituvaa myrkyllisyyttä eli valotoksisuutta, käyttäen malliaineena reteeniä (7-isopropyyli-1-metyylifenantreeni), jota esiintyy runsaasti sellu- ja paperiteollisuuden alapuolisissa sedimenteissä ja leviävissä jätevesipäästöissä.

Related to ozone depletion, 20-50 % increases in CIE-weighted UV-B doses have been predicted in northern latitudes in coming decades. In order to investigate whether increased UV-B radiation is a risk factor for the most sensitive larval stages of freshwater fishes (vendace, whitefish and pike) a series of experiments were conducted under lamps in the laboratory and under the sun in the field. Besides direct effects of UV-B, phototoxicity of certain environmental xenobiotics may also follow. The possibility of phototoxicity of retene, a resin acid derived PAH, was investigated. UV-B conditions considered to be realistic in the future were strictly followed. UV-B alone, even at high dose rates, had only minor effects on coregonid larvae, indicated a minor sunburn reaction of the skin, reversible growth response and increased pigmentation. However, pike larvae were highly sensitive to UV-B under laboratory conditions even in current doses, indicated as severe neurobehavioral disorder. Monitoring of animals with the behavioral syndrome revealed substantial late mortality. Interestingly, field experiments with pike suggest that only minor increases in ambient UV-B coming on the earth's surface may cause sublethal effects to larval fish. However, the frequency of behavioral disorders was considerably lower in the field than under laboratory conditions. Newly hatched larvae of whitefish, vendace and pike differed substantially in their reactions to UV-photoinduced toxicity of retene. By itself, retene - when tested up to 100 µg/l - had no short-term toxic effects to the larvae of boreal fishes. In coregonids, however, the combined exposure of retene+UV resulted in dramatic lethality at low concentrations of retene in acute (72 h) exposures. On the other hand, retene had no phototoxic effects to the larval pike. Overall, it can be concluded that for post-hatch larvae of whitefish and vendace the synergism of UV-B and retene is a key factor of potential ecotoxicological risk to be taken into consideration in lake areas chemically contaminated by sources of retene.