1. The slide show was designed and produced for the NMA by STEP, the
Science Training &
Education Partnership
Training &
Science
Education
Partnership
The material in this slide show is provided free for educational use only. All other forms of storage or reproduction are subject to copyright- please contact the National Marine Aquarium

2. Toxic materials in marine food-webs

3. Toxic materials
Where they come from
Summary
Where they end up

4. Toxic materials
Where they come from
Summary
Where they end up

5. Many different types of toxic materials enter the marine environment
There are several natural sources for some toxic materials such as heavy metals and cyclic hydrocarbons. Other materials have no known natural source

6. Some are natural, but most are man-made

7. The list includes: ‘Heavy’ metals such as mercury and cadmium
Pesticides such as DDT and lindane
Some toxic materials fitr in more than one of these categories. For instance, the pesticide mirex has also been used as a fire-retardant
Industrial compounds such as some lubricants and fire-retardants
Combustion products such as dioxins

8. High levels of these toxic materials will kill animals
However, normal levels in the environment are low
For many toxic materials, it is often difficult to measure environmental loevels

9. At low levels, there are still effects on animals
These effects include cancers and reproductive changes
Effects on animals may be demonstrated at tissue concentrations of microgrammes- or even naogrammes-per kilogramme body mass
Many organic toxic materials mimic natural hormones, so create disruption in the endocrine system. Some of these are oestrogen mimics, causing marked effects on male mammals

10. This means that they last for a long time
Toxic materials are often very slow to break down in the environment and in living things
This means that they last for a long time
Many of these materials are designed specifically to be long-lasting, so they persist in the environment
They are slow to break down in living things, and intermediate breakdown products may themselves be toxic

11. Toxic materials
Where they come from
Summary
Where they end up

12. Few toxic materials enter directly into the marine environment
Most come in from the land and via the atmosphere

13. Local sources include:
Pesticides applied in coastal agriculture
Anti-fouling treatments applied to ships
Disturbance of polluted sediments by dredging
Marine pollution incidents such as shipwreck
Anti-fouling treatments are designed to stop plants and animals growing on ships’ hulls and other marine structures. The most notorious compounds are organo-tin materials, such as tri-butyl tin, which have caused major impacts in some areas close to shipyards where they have been applied

14. Transport from inland occurs by:
Run-off and rivers
Transport through the atmosphere
Migration of animals
Shipping
The importance of different long-distance transport mechanisms depends on the solubility and vapour pressure

15. “Cold condensation’ occurs where the vapour pressure of a compound is sufficient for it to evaporate in warms air, but not in cold. This means that these materials tend to accumulate in cold environments
UNEP / Frank Wania

16. This means that they move polewards
Toxic materials that are transported in the atmosphere will tend to evaporate in warm areas and condense in cool areas
“Cold condensation’ occurs where the vapour pressure of a compound is sufficient for it to evaporate in warms air, but not in cold. This means that these materials tend to accumulate in cold environments
This means that they move polewards

17. Toxic materials
Where they come from
Summary
Where they end up

18. Toxic materials enter the marine food-web largely at the bottom of the food-chain - the producers
Many toxic materials condense onto particles, so that they enter the food chain via phytoplankton

19. These are then eaten by herbivores
In turn, they are eaten by predators

20. These graphics indicate the build-up of toxic materials in predators
These graphics indicate the build-up of toxic materials in predators. Note that the predator will eat several times its own body mass to fuel respiration and growth. In many cases, the entire toxic burden of its food will be retained
Each copepod contains a small amount of toxic material from its plant food
STEP

21. The fish stores most of the toxic material from its food
STEP

22. The more copepods that it eats, the more toxic material is stored
STEP

23. In turn, predators further up the food chain build up even higher levels of toxic materials
The small plankton-eating fish from the last slide can be eaten by a larger predatory fish, which in turn can be eaten by a fish like a tuna or a shark
Concern has been raised about heavy metal levels in marine predatory fish eaten by humans, such as swordfish, marlin and tuna

24. For some toxic materials, top predators in polar ecosystems show especially high levels
Many well-documented studies indicate the accumulation of pesticides in polar marine mammals and birds. This is especially true for volatile compounds where ‘cold condensation’ (see slide 14) means that these compounds are gradually accumulating in polar ecosystems

25. Toxic materials
Where they come from
Summary
Where they end up

26. You have seen that -
Various toxic materials enter the marine environment
Many of these come from the land or via the atmosphere

27. You have seen that -
Toxic materials enter the food chain mainly through the producers
Top predators in a food chain build up highest levels of toxic materials

28. www.justaddh2o.tv www.national-aquarium.co.uk NOTES for USERS
The material in this slide show is designed to support the teaching of science at Key Stage 1
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