Arsenic – a hidden threat in food

The Ganges River extends across 2,500 km from the eastern Himalayas to the Bay of Bengal and is considered one of the most polluted rivers in the world. When it overflows, the flood waters spread cholera and other epidemics in the extremely densely populated areas of northeastern India and Bangladesh. Western aid agencies wanted to remedy this.

“They started a major project to drill wells in the area,” says Markus Tamas, professor of microbiology. “But they didn’t drill deep enough, and the bedrock in the area is very rich in arsenic, a toxic metal.”

The odourless and tasteless metal seeps into well water, and more than 10 years after the wells had been drilled, the effects of arsenic began to appear. People in the area exhibited skin lesions, which are a sign of chronic arsenic poisoning.

“The catastrophe was a fait accompli. Up to 70 million people in Bangladesh may be affected, making it the world’s largest mass poisoning.”

For 20 years, Markus Tamas has studied how various toxic metals make their way into cells, why they are toxic for cells and what cells can do to defend against them. People have long known that metals have a variety of effects on us and on our health, but we haven’t known why this is so. For example, for a long time it has been known that silver has an antibacterial effect.

“In the past wealthy people bought silver vessels and kept water in them to purify it. So even though we have known that metals affect health, we have failed to understand this in detail.”

In his research Markus has focused on arsenic and cadmium in particular. Both metals are present in the environment, are toxic and have no biological function. Arsenic can cause cancer and affect the skin and skeleton as well as kidney function. A person exposed to the metal at an early age can suffer brain damage, and it may be responsible for neurodegenerative diseases such as Alzheimer’s and Parkinson’s.

Proteins are necessary for bodily processes to function properly, and for proteins to function properly, they must have a three-dimensional structure. Toxic metals affect the ability of proteins to assume this structure, which in turn affects the functioning of cells and longevity. Clumps of protein are formed, and their accumulation can contribute to ailments such as dementia.

“But while it’s true that arsenic causes cancer, it can also be used to treat some forms of cancer,” Markus points out. “A certain type of blood cancer is characterised by cell division that is out of control. Arsenic binds to a protein that controls cell division, breaking down the protein and thereby inhibiting cell division.”

Another major reason that so many people are already poisoned by arsenic or run the risk of poisoning is rice. The crop that is a staple in the diet of over three billion people is unfortunately very good at absorbing arsenic. As a result, rice constitutes a health hazard when it is grown in areas rich in arsenic. And the risk may also be present in areas where arsenic is not found naturally in the bedrock. Some parts of the United States where cotton was previously cultivated are rice paddies today. When cotton was still being grown in these locations, products containing arsenic were applied to remove leaves from the plants before harvesting the cotton.

“They sprayed crops with this substance for many years, and today one can find arsenic in rice growing there.”

Two proteins are particularly important with respect to the different ways cells protect themselves against arsenic and other toxic metals. One lets in arsenic through the cell’s outer layer, the membrane. The other protein controls how much arsenic is allowed into the cell. Markus Tamas compares this with the opening and closing of the door to the cell’s interior.

To counteract the absorption of arsenic by rice, it’s possible to manipulate the proteins of plants growing in the area so that they open the door for the arsenic. In this way they suck up the arsenic found in the ground and cleanse the soil of toxic metals. The plants can then be discarded, and the soil can be used to grow rice. The collective term for this method of cleaning up contaminated soil is phytoremediation, and there is great interest in it within the biotechnology field.

“There is also a project under way in the opposite direction – manipulating proteins in plants so that they keep the door closed to the toxins. It doesn’t matter if arsenic is present in the ground as long as it is not able to enter the plant.”

In his future research Markus Tamas is pursuing two main lines of inquiry. One is to examine extremely unusual metals used in new high-tech products whose potential health effects are largely unknown to us. He mentions the metals indium and gallium, which are used in products such as computer monitors and solar cells. When the products are discarded, they often wind up in landfills in the Third World, where the metals can leach out and expose people who want to extract the metals. There is a fear that this could be a ticking time bomb for health.

He also wants to conduct more research into how cells develop resilience through various mechanisms.

“We are focusing on a protein that acts as a molecular sensor. It detects when arsenic enters the cells and activates parts of defence mechanisms. What is it these sensors detect? Is it the metal itself, or is it something that the metal releases? And what happens to these sensor proteins that causes them to trigger the cell’s defence systems?”