I've not see much data, but here's a review which suggests your levels may not be high enough for substantial effects, but may be getting close.:
http://www.ivl.se/download/18.343dc99d14e8bb0f58b7417/1445515506056/B1486.pdf
The toxicity of selenium to aquatic organisms. Turner and Rudd (1983) summarised older (1959-1983) literature data on the toxicity of Se to aquatic biota (table 2). They found a wide range on acute toxicity values, 96-h LC50 values for zooplankton, for instance. varied between 0.12 and 183 mg l-1. The lowest effect level reported in their summary was 50 µg l-1,. at which concentration growth of certain species of algae was reduced. The speciation of the added Se is not mentioned in the latter study. while selenite was added in the other studies. The importance of the speciation of both the Se and the test organism was demonstrated by Ingersoll et al. (1990). Seleno-L-methionine was extremely toxic to daphnids (Daphnia magna); mortality was 50 to 70% after 48h at concentrations of 4 to 8 g l-1, while acutely lethal concentrations for midge larvae (Chironomus riparius) were about 1000 times higher (5.78 mg l-1). The 48-h LC50 values for both species exposed to selenite or selenate ranged between 0.7 and 16.2 mg l-1. At long term exposure (21- 30 days) to a 6: 1 mixture of selenate to selenite, the emergence time of adult midges was delayed at Se concentrations ≥ 837 µg l-l, while growth of adult daphnids was reduced at Se ≥ 156 µg l-1. A maximum acceptable toxicant concentration for selenite between 44 and 93 µg l-1 was indicated for growth and viability of juveniles of the marine amphipod Allorchestes compressa exposed to sodium selenite and to (Ahsanullah and Palmer, 19801 Ahsanullah and Brand 1985). Selenium at the same concentrations in mixtures of sea water and seleniferous leachate from coal fly-ash (5% leachate) was less toxic than the pure sodium selenite. The concentrations that lead to acutely toxic effects on the amphipod were more than ten-fold higher. Ornes et al. (1991) found reduced growth in floating aquatic plants at water concentration <2.5. mg Se l-1, added as sodium selenate. The selenate ion is also a competitive antagonist to sulphate at sulphate reduction by bacteria, resulting in growth inhibition for the bacteria (Postgate, 1984).
