Question

A community lives in a remote area next to a lake and they rely on the fish in the lake for food. They are concerned that the fish they are catching from the lake have been contaminated with mercury. The lake has an area of 30,000 m² and an average depth of 10 m; it is fed by a river with flow 25 m³/s. Assume that 5% of the flow entering the lake is lost to evaporation. Some mercury enters the water naturally from the soil upstream of the lake. The mercury concentration in the river upstream is 0.07 ng/L. A small gold mining operation uses mercury or “quicksilver” to extract more metal. The runoff, which has a mercury concentration of 0.82 ng/L makes its way into the lake with a flow of 1 m³/s. Additionally, dry deposition of mercury from atmospheric aerosols adds mercury to the lake at a rate of 12 ng/s. The lake is drained by the river flow.

1. Calculate the steady-state concentration of mercury in the lake (ng/L), assuming the lake is well-mixed.
2. Assume the bioaccumulation factor for mercury is 220 L/g for the fish that the community eats. Local health officials recommend eating fish only if the mercury concentration is below 2 µg/g of fish tissue. Should the community be concerned about eating the fish?

Answer 1

ANSWER:--

STEADY STATE CONCENTRATION:--  Steady-state concentration (C ss) is defined as the time during which the concentration remains stable or consistent when the drug is given repeatedly or continuously (IV infusion). The time to reach steady-state is a function of T ½ and is achieved when the rate of the drug entering the systemic circulation equals the rate of elimination.