1. Hello,
I have some questions about ecotoxicology. I need to solve these problems but I really don't know how to start..

1. A well-biodegradable insecticide is dosed annually at 0,3 active compound/ha. This compound goes 5cm deep in the soil and is suspected to be toxic for soilinvertebrates. There's only 1 NOEC known, namely 50µg/L for Daphnia magna. The insecticide has a half live of 10 days, the LogKoc=3.0, water solubility is 100mg/L and the soil has 2% organic carbon.
Is there a risk on short-term for the invertebrates and if so, how long does it take untill the risk can be excluded?

2. The concentrations pentachlorophenol (PCP) in a contaminated stream is 15 µg/L (total concentration). Only the acute LC50=0,4mg/L is known at pH 5,5 for a species of fish. The water in the stream has a pH=7,5, and contains 15mg/L suspended solids (fraction organic carbon=0,04).
Find out whether the concentration PCP in the disolved fraction is a risk (PEC>PNEC). You can assume that the toxicity and the sorption of phenol (HA) is 100 times higher then phenolate (A-). The pKa of PCP is 6,7.

3. A test is done to measure the BCF of pentachlorophenol (PCP) for a fish. The testing water has a pH=5,5. The fish is placed in the container and after 24 hours of contact (constant external concentration of PCP=1µg/L), the internal concentration equals 825µg/kg fresh weight. After this, the fish is placed in another tank for a depuration test in uncontaminated water. After 48h of depuration there is only 45% PCP left in the organism.
Calculate the BCF for this organism in this testwater. What is the BCF for this species in a surfacewater with pH 7,5 , suspended solids 15mg/L (fraction organic carbon = 0,04). You can assume that the toxicity and the sorption of phenol (HA) is 100 times higher then phenolate (A-). The pKa of PCP is 6,7.

4. The PNEC for Cd in fresh water is 0,2µg/L, expressed as Cd in the dissolved fraction of water. Chronical data of Cd toxicity is not much available, and they want to use the PNEC of Cd of freshwater for marine waters. The concentration of Cd at sea is 2µg/L, expressed as Cd in the dissolved fraction.
Is this concentration above the PNEC if you assume that the chemical activity of free Cd (Cd2+) is the same for marine as fresh water organisms? In fresh waters, 80% of the dissolved Cd appears under the form as free Cd2+ and the ionic strength equals 10^-3M. At sea the concentration of chloride (Cl-) equals 0,4M and the ionic strenght equals 0,45M.

5. A river sediment contains 2µmol AVS/g d.s. and the environmental background toxical metals, measured as SEM, is 0,5 µmol/g ds. A galvanisation company drops the sink in the surfacewater and the inspection measures a rise of 130mg Zn/kg ds in the sludge at the point of emission. There is also a rise in Cu in the sludge and equals 65 mg Cu/kg. That rise is caused by a company a few kilometers further away. The sediment contains 1% organic carbon.
Is there a risk in the sediment? If so, is it caused by mixture toxicity or is there only one metal responsible for the effect? (Atomair weight Zn: 65,4; Cu=63,6).

and my apologies for the crappy English, it's not my native language.

2.

3. For example, I'd like to know how you can covert a LC50 from one pH to another one?

4. From the Earth sciences subforum:

http://www.thescienceforum.com/Homew...ING-15400t.php

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