 Planet Earth is blue. Over 70% of its surface is covered by water. From space it does indeed look blue. Close up, the reality is very different. The pollution, rubbish and waste we create at sea and on land ends up on our shores and in our oceans. We're destroying a precious resource one we depend on so much for food, work and play. Marine pollution has many victims. Millions of people depend on the fishing industry for their income and food. If contamination in the sea reduces fish stocks there's less to sell and less to eat. The pollutants in the oceans absorbed by plankton and fish could eventually make their way to the top of the food chain. That's us. Decades of development and growth may have improved our quality of life but we've been careless with the byproducts of this growth. We need to understand more about the impact of pollution to be able to manage it better and prevent it. This is where the International Atomic Energy Agency the IAA plays a key role. At the agency's laboratories in Monaco nuclear and isotopic techniques are used to conduct research into marine pollution, its causes and impacts. So what are isotopes? All matter on earth is made of elements. An atom of an element is made of protons, neutrons and electrons. The number of neutrons in an atom may vary. Atoms with different numbers of neutrons are isotopes of a specific element. Isotopes can be heavier or lighter. Some isotopes are stable and don't change. Radioactive isotopes or nuclides decay over time and emit ionizing radiation. Most isotopes occur naturally. We can't see them but with the right instruments we can measure them. Radiation from decaying isotopes can be detected using an alpha, beta or gamma spectrometer. By measuring this radiation the scientists can identify which radionuclides are present in a sample and their concentrations. For stable isotopes, mass spectrometry is used. Through their difference in weight, isotopes can be swiftly and precisely detected giving information about types of pollution, its level and source. Scientists from the IAEA and its partner institutes analyse isotopes in samples collected from the sea or coastlines. They're trying to find out whether toxic elements are in places or organisms where they shouldn't be or above the recommended limits. Radioisotopes can be used to trace a biological or chemical process. For example, to see how marine life accumulates the toxic heavy metals commonly found in the sea a radioisotope of mercury can be added. It mixes with the mercury already in the water. Since it can be detected its behaviour becomes visible to the scientists. Nuclear techniques can also be used for dating. Samples are taken from the bottom of the sea. A radioisotope decays over a specific period of time. By measuring its activity in a core sample it can be determined when the different sediment layers were deposited. With this information the scientists can specify when incidents of pollution occurred. Planet Earth may no longer be blue but our oceans and shores will continue to be an essential part of our daily lives for centuries to come. Maintaining their health is key to our future. By using the results gained from the IAEA's research projects worldwide we can learn how to use the oceans with respect rather than abuse them.