Dental waste containing high levels of toxic mercury is being pumped into the public sewage system across the country, an academic study shows.
A study of 38 wastewater samples from Abu Dhabi and Sharjah dentists found an average concentration of mercury was about 318 micrograms per litre (µg/l).
High levels of amalgam, used in metal fillings, could harm the community, said Dr Sausan Al Kawas, the head of oral and craniofacial health sciences at the faculty of dentistry at Sharjah University.
"Dental amalgam is of a particular concern because almost half of its mass is mercury, a metal that has well documented health risks."
"According to Dubai Municipality's environmental standards the maximum allowable limit for discharge of mercury containing waste into the sewage system is 10 µg/l," Dr Al Kawas said
Dr Al Kawas said several studies had shown that exposure to mercury may lead to several health complications such as impairment of the developing central nervous system and lung and kidney damage.
The regulations for mercury waste vary by emirate.
However, a spokesperson from the Abu Dhabi Sewerage Service Company (ADSSC) said the level of mercury discharged from sewerage-treatment plants into the water supply had not reached those levels.
"Our equipment allows us to test down to .005 milligrams [5µg] per litre at our two waste water premium plants, and we have never detected that much," he said.
"Requirements for discharging such substances back into the water stream state that substances cannot contain more than .001 milligrams [1µg] per litre."
The spokesperson added that it was possible that the mercury is diluted after it mixes with other waste as it arrives at the water-treatment plant.
Dr Al Kawas said dental clinics should adopt measures to reduce their mercury discharge, such as the use of amalgam separators and filters, improving the design of their discharge system, and cleaning their equipment with high-pressure water cleaning.
The UAE's 1999 waste management law requires that medical waste be disposed of in a manner that does not harm the environment or the community.
It governs the policies set by each emirate's municipalities and health authority. Abu Dhabi's policy, for example, set in 2007, requires that every health care facility provides the required resources for proper waste management at its premises. This includes colour-coded bags and containers with the biohazard symbol for categorising waste.
All staff handling such waste must be continuously trained by the health care facilities on how to follow the health authority's guidelines. The policy also states that there must be a biannual meeting with the outsourced companies which are collecting and disposing of the waste. What was lacking, Dr Al Kawas said, was a specific law that requires dentists to install filters in their drainage systems.
"Because there are no such regulation, there are no penalties being issued. So dentists just dispose of amalgam in the sink. As a result, this enters the sewage system," she said.
Some dentists have stopped using mercury amalgam altogether, preferring alternatives in part because of the difficulty of processing the waste.
Professor Najeeb Al Khaja, secretary general of the Shaikh Hamdan Bin Rashid Al Maktoum Award for Medical Sciences, which supported the study, said the findings were being flagged to the authorities.
"We have informed the health authorities and municipalities so that they can take the required action and prevent mercury from reaching our food and water," he said.
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