**4. Ecological risk assessment by sediment quality guidelines**

Over the last two decades, a considerable amount of research effort has been put into investigating sediment toxic threshold levels [79, 80]. As a result there are now a number of international guidelines relating to toxic concentrations as determined by field and laboratory data. The work of Long et al. [79] on sediment quality guidelines (SQGs) provides a useful tool for screening sediment chemical data to identify pollutants of concern and priorities problem sites (x). In their study, the toxicity range of these chemical pollutants in the sediments was estimated from experimental studies in the laboratory, observation, and measurement of these parameters in the field. The finding of the work can estimate the level of two pollutants that have high chances to give impact in adverse biological effect of 10 and 50% of biota population.

 Using this approach, scientists classified the toxicity of metals into effect range low (ERL) and effect range median (ERM) concentrations [79]. The concentration value between ERL and ERM represents the intermediate range in which this concentration can give an impact in 10–50% of the organism populations. ERL indicates the chemical pollutant can be considered to be of minimal or low concern, and the adverse effects toward organisms are infrequently observed (<10%

#### *Monitoring of Marine Pollution*

impact on organisms population) if the concentrations are below the ERL value. On the other hand, ERM indicate that if the concentration is above this level which the significant effect can be observed in 50% or more of the organism population considered to be toxic and of significant concern.
