Miankaleh International Wetland: toxic element hazards and possibility of botulinum poisoning

Miankaleh Wetland, located in the southeast of the Caspian Sea, is a rich ecosystem and an international haven for wintering of migratory waterbirds in Asia. Moreover, it is the most important caviar producing area in Iran. This wetland has attracted great attention due to the death of thousands of birds and fish related to Clostridium botulinum poisoning in recent years. Considering the limited previous studies in Miankaleh Wetland, which were confined to sampling sediment in a limited number of stations and continuous input of pollutants, further research on sediments and water of this wetland is essential. So, this study aimed to evaluate the physicochemical features of water and sediments as a key indicator in botulinum poisoning, occurrence of potentially toxic elements (PTE), sources and environmental hazards. For this purpose, 95 and 40 site selected for sampling of sediment and water, respectively. Results showed that most of water samples exhibit low dissolved oxygen, low redox potential, and relatively high pH and electrical conductivity (EC) with mean 7.82 mg/l, 63.69 mV, 8.3, 15.10 mS/Cm, respectively. Also, sediment samples contain high organic matter and high EC, with mean 9.01 % and 13.29 mS/Cm, respectively. So, botulinum contamination is a possibility based on the physicochemical properties of water and sediments. Maximum concentrations of some PTE in Miankaleh water exceed the corresponding safety thresholds. And also, the maximum concentrations of all PTE in the sediment samples exceed the background and Caspian Sea sediment value. Based on SOM, PMF analyses, and sequential extraction results there are three major contributors of PTE in Miankaleh Wetland. But PTE contamination does not appear to be a likely factor in birds and fishes poisoning. However, to prevent future disasters, it is crucial to manage wastewater entering Miankaleh Wetland to preserve the physicochemical properties of the water and sediment.