Thousands of microrobots controlled by magnets could help remove heavy metals from contaminated water. The microbots are made from iron oxide-coated mushroom spores, and cause heavy metal ions to cling to the pores they come into contact with. Once theyve been placed into contaminated water, an external magnetic field is used to move the microrobots around. They and the heavy metals clinging to them are then recovered from the water using the same magnet. These magnetic spores gather into a small area, form a pattern, then we use the magnetic field to do the navigation, says Li Zhang at the Chinese University of Hong Kong. Heavy metal is a problem. Toxic metals, including lead, can cause serious health issues, if they leak into water ways. According to the Institute for Health Metrics and Evaluation at the University of Washington, lead exposure accounted for 540,000 deaths worldwide in 2016. In an experiment, the microbots reduced the amount of lead in contaminated water from five parts per million (ppm) to 0.9 ppm within 50 minutes of treatment. That is very far away from the drinking water standard or the environmental quality standard, says Scott Young at the University of Nottingham. Lead can be at no higher than 0.01 ppm in drinking water in the UK to be considered safe, for example. But Zhang says that the aim of the project isnt to treat water with higher levels of lead, but to reduce contamination from a lower starting point.
New Scientist, 18 November 2018 ; http://www.newscientist.com/