is observed at 8-15 mg/liter. According to resistance, green algae and 

 diatoms are intermediate. In blue green algae, reproduction ceases at 100 

 mg/liter and in diatoms at 200 mg/liter. 



Complete inhibition of photosynthesis in all algae occurs at concen- 

 trations from 700 to 1400 mg/liter. Resistance of algae to phenol is to a 

 considerable degree determined by the composition of the medium. The 

 richer the medium in nutrients, the more resistant are the algae grown on 

 it. 



Chlorella has been studied in more detail. Inhibition of its growth 

 commences at 100 mg/liter. At 1500 mg/liter reproduction ceases. The 

 toxic effect of phenol is directly proportional to the light intensity. 

 Resistance of various strains of Chlorella is determined by their sensi- 

 tivity to light. Respiratory processes in Chlorella are more tolerant to 

 the influence of phenol than photosynthetic processes. 



INVERTEBRATES 



Different crustaceans, molluscs, aquatic insects and arachnids were 

 used as experimental organisms. Resistance of invertebrates to phenol 

 varied widely: At 48 hrs exposure and a temperature of 20 C, LC50s fluc- 

 tuate from 2 to 2000 mg/liter; however, the organisms may be divided into 

 three groups (Table 1) according to their resistance. 



There are low resistance invertebrates--larvae of caddis flies (genus 

 Trichoptera ), stoneflies (order Plecoptera ) , mayflies (order Ephemerop - 

 tera ), beetles (order Coleoptera ), damselflies (order Odonata ), blackflies 

 (order Simuliidae ) and crustaceans (suborder Cladocera ) . Their LC50 are in 

 the range of 2-50 mg/liter. 



Invertebrates of intermediate resistance are larvae of culicidflies 

 (family Culicidae, Subfamily Orthocladiinae) , order Megaloptera and image 

 bugs (genera Sigara, Gerris). Their LC50s are in the range of 50-300 

 mg/liter. 



There are highly resistant invertebrates--larvae of other flies (with 

 the exception of the families Simuliidae, Culcidae, subfamily Ortho- 

 cladiinae), image bugs (with the exception of the genera Sigara, Gerris), 

 of beetles, molluscs, spiders and mites. Their LC50 are in the range of 

 400-2000 mg/liter. Aquatic invertebrates with respect to their resis- 

 tance to other toxic substances (pesticides) are arranged approximately in 

 the same order. 



A comparison of the resistance of organisms indicates that Sida crystal - 



Tina from the Cladocera family may serve as a susceptibility test-object 



for toxicological investigations. This organism, like Daphnia, is easy to 

 rear under laboratory conditions. 



182 



