e-waste problem is further exacerbated by the fact that many countries and corporations lack recycling programs for ASIC chips. Developing a recycling infrastructure for bitcoin mining may prove to be beneficial, though, as the aluminum heat sinks and metal casings in ASIC chips can be recycled into new technology. Much of this responsibility falls onto Bitmain, the leading manufacturer of bitcoin, which currently lacks the infrastructure to recycle waste from bitcoin mining. Without such programs, much of bitcoin waste ends up in landfill along with 83.6% of the global total of e-waste. Many argue for relinquishing the proof-of-work model altogether in favour of the proof-of-stake one. This model selects one miner to validate the transactions in the blockchain, rather than have all miners competing for it. With no competition, the processing speed of miners' rigs would not matter. Any device could be used for validating the blockchain, so there would be no incentive to use single-use ASIC chips or continually purchase new and dispose of old ones. Environmental impact A recent study about the rising electronic pollution in the USA revealed that the average computer screen has five to eight pounds or more of lead representing 40 percent of all the lead in US landfills. All these toxins are persistent, bioaccumulative toxins (PBTs) that create environmental and health risks when computers are incinerated, put in landfills or melted down. The emission of fumes, gases, and particulate matter into the air, the discharge of liquid waste into water and drainage systems, and the disposal of hazardous wastes contribute to environmental degradation. The processes of dismantling and disposing of electronic waste in developing countries led to a number of environmental impacts as illustrated in the graphic. Liquid and atmospheric releases end up in bodies of water, groundwater, soil, and air and therefore in land and sea animals – both domesticated and wild, in crops eaten by both animals and humans, and in drinking water. One study of environmental effects in Guiyu, China found the following: Airborne dioxins – one type found at 100 times levels previously measured Levels of carcinogens in duck ponds and rice paddies exceeded international standards for agricultural areas and cadmium, copper, nickel, and lead levels in rice paddies were above international standards Heavy metals found in road dust – lead over 300 times that of a control village's road dust and copper over 100 times The Agbogbloshie area