The toxicity of marine pollutants is evaluated through bioassays by a) calculating the concentration at which 50% of the test organisms of a particular species die b) determining the length of time the pollutant remains in the environment c) estimating the number of trophic transfers in the food web affected by the pollutant d) determining the total biomass of affected organisms in the environment

a) calculating the concentration at which 50% of the test organisms of a particular species die

Explanation:

Bioassays -

Bioassays is an analytical method to assess the effect of marine pollutant on the organism by estimating the concentration at which 50% of the test organisms die after exposing the test organisms for a specified time.

It can be done  by quantitative or by qualitative experiment , or direct or indirect .

It is used to detect the biological hazards or give the quality assessment of the mixture .

It is also used for the monitoring the quality of water .

a) calculating the concentration at which 50% of the test organisms of a particular species die

a. it led to stricter immigration laws.