Iodine in the environment of the High Atlas Mountain area of Morocco

The Ounein Valley in the Atlas Mountains of Morocco has been studied as part of an investigation into the environmental controls in iodine deficiency disorders (IDD). The area was identified from earlier sociological studies that highlighted the area's serious problems with iodine deficiency disorders. In the 1990's it was an area where the under- five mortality rate exceeded 25% and dietary deficiency of iodine reached more than 90% in some villages. Soil, drinking water, and locally grown crop samples have been collected to determine the iodine status of the environment. These results are compared with a control area near Agadir where there is low prevalence of IDD. In the coastal Agadir area average iodine levels in surface soils are 2.76 μg/g I compared to 1.47 μg/g I in soils from the Ounein Valley some 150 km inland. The water-soluble component of the soil, considered as the mobile bioavailable fraction, is higher in the Agadir area than the Ounein Valley with average values of 0.12 and 0.04 μg/g I respectively. There is three times more "available iodine" in the soils of the Agadir area than in soils of the high IDD prevalence Ounein Valley. Iodine in soils decreases away from the seacoast although both low and high iodine soils are found in the coastal zone. Although the iodine levels in the soils from Ounein Valley are lower in iodine, they are not significantly different from soils from other parts of the world. The difference in iodine status of the environment is best indicated by iodine in drinking water - 17.8 and 1.6 μg/l for Agadir and Ounein respectively, i.e. a tenfold difference. The correlation between low iodine drinking waters and IDD prevalence is seen in many parts of the world and a < 3 μg/l I threshold is suggested as an indicator for an iodine deficient environment. Interpretation of crop iodine results is limited by the fact that it was not possible to compare like with like. Wheat and barley grains were sampled in the Agadir area whilst vegetables were collected from the Ounein Valley. Beans (mean 9 μg/kg) growing in the same field as carrots (mean 25 μg/kg) were consistently found to contain less iodine than the carrots which still only contained 0.75 - 3.58% of the total soil iodine. The levels of iodine in barley grains ranges from < 10 - 25 μg/kg and the sample of wheat contains 40 μg/kg I (all results for dry matter). Salt samples bought in the local market were also determined for iodine and contents were considerably less than that advertised. However, even with lower contents, iodised salt contributed substantially more iodine to the diet than uniodised salt. If locals were totally dependent on their local environment for providing iodine, then the diet would be substantially lacking in iodine, a situation that would probably been seen in most non-coastal districts of the world. However, poor development with lack of access to external food sources has greatly increased the risks of IDD to which the local population will be exposed. Improved road access and development in the region in the past five years has clearly reduced the risks. Because most of the Ounein Valley is dependent on irrigation to grow crops, the addition of iodine to irrigation waters could potentially help improve the environmental iodine status. However, the poor sandy soils of the area with little organic matter reduces the soil's ability to fix iodine, whether it be natural iodine deposited from the atmosphere or iodine added to irrigation waters.