From a biological point of view, as noted earlier, the most significant radioactive substances in the emissions from the accident were iodine, caesium, strontium, and plutonium.
Different problems arise with different radioactive substances. Radioactive iodine is short-lived and practically had disappeared some weeks after the accident. Its significance is due to the fact that, if inhaled or ingested, it accumulates in the thyroid gland, where it may deliver large radiation doses as it decays. The doses may result in impaired thyroid function and, many years after the exposure, in thyroid cancer. The difficulty about radio-iodine is that its original distribution can no longer be measured but must be inferred.
Caesium is the element that clearly dominates the long term radiological situation after the Chernobyl accident. Due to its penetrating radiation, caesium deposited on the ground may give an external dose. It may also enter the food chain and give an internal dose. It is eliminated metabolically in a matter of months. Caesium is relatively easy to measure.
Plutonium and strontium, on the other hand, present difficulties in measurement; but there is relatively little strontium in the fallout and it does not give a dose unless ingested or inhaled. Very little plutonium travelled far from the reactor site, and because of its chemical stability, it does not find its way easily into food chains.
Measurements and assessments carried out under the project provided general corroboration of the level of surface contamination for caesium reported in the official maps that were made available to the project in the USSR. Analytical results from a limited set of soil samples obtained by the project teams, near the evacuated zone, corresponded to the surface contamination estimates for plutonium. However, project results were lower in the case of strontium
The concentration of radionuclides measured in drinking water and, in most cases, in food from the areas investigated, were significantly below guideline levels for radionuclide contamination in food moving in international trade and in many cases were actually below the limit of detection. The analytical capabilities of Soviet laboratories appeared to be adequate. The range of performance of the Soviet laboratories that participated in the intercomparison exercise was broad, but similar to that found in previous international comparison exercises. The few problems identified, including the tendency to overestimate strontium, did not significantly affect the use of data for purposes of making conservative dose assessments.
The extensive surface water sampling programmes in the USSR are adequate. Certain problems during sampling and analytical procedures could result in the possible overestimation of the concentration of radionuclides in water.
Insufficient information was available to evaluate air sampling equipment and procedures. Although the relative contribution to radiation doses of some resuspension of radioactive materials in the air (as dust) is believed to be minor, it should be noted that the occurrence of such airborne resuspension, particularly during agricultural activities or dry periods, cannot be excluded.
Rapid screening and sophisticated techniques used locally for monitoring commercially available food from production to consumption appeared to be satisfactory. The relevant instrument calibration technique could not be evaluated sufficiently by the project owing to the lack of detailed technical information.
The radioactive contamination of food samples was found to be in most cases below the levels established by the responsible authorities for specific countermeasures in the settlements surveyed. In some settlements, milk from individual farms and food collected in contravention of official recommendations could be contaminated above these levels.
Some technical recommendations about analytical methods used by Soviet scientists were made and, in particular, it was felt by the Committee that there should be fuller participation in the future with international intercomparison programmes and intercalibration exercises.