The underlying problems associated with the development of the biotic ligand model (BLM) for prediction of silver toxicity, and its associated physiological and toxicological endpoints, were investigated at a mechanistic, physiological level in juvenile rainbow trout. An equilibrium level of silver accumulation at the gills is achieved over time during flow-through exposures. The pattern of peak and decline in accumulation during static exposures is due to a decrease in the bioavailability of Ag⁺ because of complexation by organic carbon produced by the fish, a consequence of the use of a static exposure system. The decrease in bioavailability leads to a decline in apical silver uptake and together with constant basolateral silver export, a peak and decline in gill silver accumulation. Inhibition of carbonic anhydrase (CA) by silver is responsible for the early decline in active Na⁺ uptake at the gills during flow-through silver exposure, while Na⁺K⁺-ATPase inhibition is associated with the later decline in uptake. CA activity is inhibited early during silver exposure when Na⁺ and Cl⁻ uptake are decreasing but Na⁺ K⁺ ATPase activity is not inhibited until later. The implication of the data that the rate limiting step in the movement of Na⁺ and Cl⁻ across the gill epithelium is the movement across the apical membrane, as well as the identical time course and degree of Cl⁻ and Na⁺ uptake inhibition provide additional evidence for a role of CA inhibition in the early decline in Na⁺ uptake. A relationship exists between short-term gill silver accumulation and inhibition of Na⁺ uptake. There is also a relationship between silver accumulation on the gills after 3 h, as well as after 24 h, and 96 h mortality. Together, the results of this thesis indicate that short-term gill silver accumulation is an appropriate endpoint for the prediction of acute silver toxicity in freshwater fish, lending support to the current toxicological version of the silver BLM. These results also indicate that the predictive capabilities of the current physiological BLM may be improved by using Na⁺ uptake inhibition rather than Na⁺K⁺-ATPase inhibition as an endpoint to predict acute silver toxicity. / Thesis / Master of Science (MS)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22973 |
| Date | 01 1900 |
| Creators | Morgan, Tammie |
| Contributors | Wood, C. M., Biology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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