The use of marine benthic diatoms in a growth inhibition test with spiked whole-sediment

The benthic diatom Cylindrotheca closterium was exposed to whole-sediment spiked with the synthetic surfactant Linear Alkylbenzene Sulphonate (LAS), as commercial mixture or individual homologues (C10-LAS, C11-LAS or C12-LAS). Separately, the diatoms were exposed to C12-LAS in a water-only system. The algal growth was determined after 72 h. The 72-h ErC50 values ranged from ≤4 to 29 mg/kg sediment, suggesting that C. closterium was sensitive to LAS. The outcomes were reproducible with a variation factor lower than 3, showing the reproducibility of the method. The test set up was cost effective, used little bench space and employed a micro-phytobenthos species that fulfilled most of the criteria for a suitable test species in sediment systems. The 72-h ErC50 obtained in a water-only system (0.141 mg/L) was ca. 2 orders of magnitude lower (0.002 mg/L). This was likely due to an indirect effect of the use of fresh sediment.