 A common definition is that recycling is a process which allows waste materials to be turned into new products and prevents the waste of potentially useful materials. Recycling reduces the use of fresh materials. It acts to reduce energy usage, reduces air pollution from incineration, reduces water pollution from landfilling by reducing the need for conventional waste disposal and has lower greenhouse gas emissions as compared to fresh material production. So with all of these benefits you must be wondering if there are any limits to a process that can have such a positive effect on the environment. Limits to recycling are often considered in terms of energy, hazards, costs and practices by individuals and countries. The biggest limit to recycling however is that not all materials can be recycled or can only be recycled a number of times before they lose their quality. Some materials once used are always going to have to be dumped as we have no method for making them useful again. What sorts of materials do you think can be recycled? See if you can come up with five. Pause the video and continue when ready. Commonly these are the materials that are recycled, glass, paper, metal, plastic, textile and electronics. How many did you get? Now let's consider the different limitations. First up is the energy aspect. Put simply some materials like paper and aluminium metal are agreed to have lower processing costs when it comes to recycling them rather than using fresh materials to make new products. However the recycling of materials like plastics is extremely energy intensive. Before the plastics can be melted and mixed together they require sorting usually by hand as there are many different types of plastics usually indicated by special marking and number. If a mixture of plastic is recycled together they either contaminate the melt or you get a lower grade of plastic than the originals which is therefore less valuable. This reduction in the quality of the recycling product is called downcycling. In addition to this there is the added complication that devices often use mixed materials. Think of a car. There are a wide range of recyclable materials, the copper wire, the aluminium in the engine, some of the plastics, the glass and the iron. However what about the alloys? These are mixtures of metals. Energy will be needed to separate these and so one of the most difficult problems of recycling is the separation of randomly intermixed particles. Secondly there are hazards to recycling including the recycling of dangerous metals. Can you think of any dangerous metals? Pause the video and name some. Continue when you are ready. Some of the metals associated with recycling are lead and mercury. Often these metals can come from the recycling of waste electrical and electronic equipment. In India and China a significant amount of pollution is generated where informal recycling in an underground economy of these countries has generated an environmental and health disaster. High levels of lead, polybrominated diphenyl ethers, polychlorinated dioxins and furans as well as polybrominated dioxins have become concentrated in the air, bottom ash, dust, soil, water and sediments in areas surrounding these underground recycling sites. Many of these chemicals become dissolved in the water that we drink called leachate. Also plants can take up these chemicals allowing toxic chemicals to enter the food chain. Finally if the chemicals are airborne there are problems with us inhaling them. There are also social issues connected to recycling. Whilst it may create jobs they are often jobs with low wages and terrible working conditions in developing countries. In areas without many environmental regulations or worker protections job-like ship breaking can result in deplorable conditions for both workers and the surrounding communities. Thirdly is the challenge for you. What do you think the cost of recycling depends on? Pause, think and continue when ready. A good answer might be that the cost of recycling depend on the efficiency of the recycling program. Governments or local authorities may not recycle because it's cheaper to use landfill. Also consumers are encouraged to recycle but this depends on people being involved in pre-sorting their recycling. Some countries or local governments impose charges when this is not done.