Aquatic Pollution and Coastal Management

Unit 5 : Heavy metal pollution

5.5.Environmental Effects
Metals may enter the systems of aquatic organisms via three main pathways (various mechanisms).
Free metal ions that are absorbed through respiratory surface (eg. gills) are readily diffused into the blood stream.
Free metal ions that are adsorbed onto body surfaces are passively diffused into the blood stream.
Metals that are sorbed onto food and particulates may be ingested, as well as free ions ingested with water.
Many organisms are unable to regulate the metal concentration in their tissues. Metals accumulate in living organisms at any time they are taken up and stored faster than they are broken down or excreted and tend to accumulate in the soft tissues (bioaccumulation).
At low concentrations many metals (Hg, Cd, Pb, As, Cu) inhibit photosynthesis and phytoplankton growth.
Slightly elevated metal levels in natural waters may cause the following sub-lethal effects in aquatic organisms:

• Histological or morphological change in tissues
• Changes in physiology such as suppression of growth and development, poor swimming performance, changes in circulation
• Change in biochemistry such as enzyme activity and blood chemistry
• Change in behaviour
• Changes in reproduction (delayed embryonic development).