On the Effect of Surfactants on the Baikal Oligochaete Mesenchytraeus bungei Michaelsen

Pollution of natural objects with surfactants is relevant, including for the lake Baikal. Here, until the near future, there was a constant increase in the tourist flow and, as a result, the ingress of these pollutants into the reservoir. First of all, the inhabitants of the littoral zone come into contact with the incoming pollutants. In this regard, the work evaluated the effect of surfactants on the survival rate of the Baikal endemic oligochaetes Mesenchytraeus bungei Michaelsen, 1901. These enchitreids are a common species. They are widespread throughout the lake from the water's edge to the deepest depths. Therefore, M. bungei is recommended as an indicator object for ecological monitoring of the lake Baikal. The tested compounds are representatives of different types of surfactants: anionic – sodium lauryl sulfate, cationic –cetyltrimethylammonium bromide and nonionic – tween-80. Baikal oligochaetes M. bungei Michaelsen, 1901 were collected in July – August 2020 in the splash zone of Lake Baikal in settlement Bolshiye Koty (South Baikal). Enchitreid about 1.8-2.0 cm long was used in the experiments. After adaptation to laboratory conditions (2 days with water aeration using a microcompressor), further incubation was carried out in glass or plastic cages with nonsterile Baikal water at a temperature of 8–10 °C and an illumination of 250-300 lux. River sand was placed at the bottom, the layer thickness of which was 0.8-1.5 cm. Baikal oligochaetes M. bungei Michaelsen, 1901 turned out to be sensitive to the anionic surfactant sodium lauryl sulfate and cationic cetyltrimethylammonium bromide at a content of 0.005-0.006 mM. So, with the addition of 0.006 mM sodium lauryl sulfate for 3 days of the experiment, the proportion of dead individuals of the test object was 40%, at 0.0125 mM – 60%, at 0.025 mM – 90%, and at 0.05 mM complete death of all enchitreid individuals was observed. Adding CTAB at a concentration of 0.005 mM increased the proportion of dead oligochaetes to 40%. TAB twice – up to 0.01 mM – led to the death of all worms. The nonionic surfactant tween-80 did not have a negative effect on the Baikal oligochaetes in the concentration range from 1 to 60 mM. The tested surfactants to reduce the degree of their effect on the survival of oligochaetes can be arranged in the following row: cetyltrimethylammonium bromide (LC100 = 0.01 mM)> sodium lauryl sulfate (LC100 = 0.05 mM)> tween-80 (harmless up to 60 mM inclusive).