Development of A Growth Inhibition Test Method Using Fresh Water Attached Diatoms

Abstract

A growth inhibition test method using fresh water attached diatoms was developed by improving microplate algal assay technique for planktonic green algae. Applying the solid culture technique for the pre-culture, using the flat bottom microplate for the test vessel and shaking the microplate at least twice a day were necessary procedures for ensuring the reproducibility of the test using attached diatoms.
Reproducible result was obtained from seven repetitions of growth inhibition tests using dimethametryn, a triazine herbicide on Achnanthidium minutissimum of attached diatom. The average ErC₅₀ values calculated from these tests was 7.9μg/l (n=7, SE=1.3).
The optimum culture condition and the adaptability as test organism were evaluated in ten kind of attached diatoms (A. minutissimum, Craticula molestiformis, Eolimna minima, Eolimna subminuscula, Fistulifera saprophila, Mayamaea atomus, Nitzschia palea, Planothidium frequentissimum, Planothidium lanceolatum, Sellaphora seminulum).
The optimum culture temperature was 15-30°C. The difference of illumination intensity (c.a.2,000lux or c.a.5,000lux) did not influence the growth rate of every diatom at the optimum culture temperature. It is concluded that C. molestiformis, E. minima, E. subminuscula, F. saprophila, M. atomus and N. palea are suitable test species in these diatoms in terms of high growth potential and that M. atomus and N. palea are valuable test species in terms of habitat diversity and easiness of isolation.