Solutions of sodium hydroxide and other chemical disinfectants may also be used, depending on the waste's characteristics. Other treatment methods include heat, alkaline digesters and the use of microwaves. For autoclaves and microwave systems, a shredder may be used as a final treatment step to render the waste unrecognizable. Some autoclaves have built in shredders. In the UK, clinical waste and the way it is to be handled is closely regulated. Applicable legislation includes the Environmental Protection Act 1990 (Part II), Waste Management Licensing Regulations 1994, and the Hazardous Waste Regulations (England & Wales) 2005, as well as the Special Waste Regulations in Scotland. A scandal erupted in October 2018 when it emerged that Healthcare Environment Services, which had contracts for managing clinical waste produced by the NHS in Scotland and England, was in breach of the environmental permits at four of its six sites by having more waste on site than their permit allows and storing waste inappropriately. 17 NHS trusts in Yorkshire terminated their contracts immediately. The company sued for compensation. Amputated limbs were said to be among 350 tonnes of clinical waste stockpiled instead of incinerated in Normanton. The company maintains that the problem is caused by a reduction in incineration capacity, and the re-classification of clinical waste as “offensive”, which meant more needed incineration. The government's contingency plans include installing temporary storage units at hospitals, but the company say that this is more dangerous than allowing them to exceed their permitted allowances. The company still has contracts with 30 other trusts in England, and a waste disposal contract with NHS England for primary care and pharmacy. In the United States, biomedical waste is usually regulated as medical waste. In 1988 the U.S. federal government passed The Medical Waste Tracking Act which allowed the EPA to establish rules for management of medical waste in some parts of the country. After the Act expired in 1991, responsibility to regulate and pass laws concerning the disposal of medical waste returned to the individual states. The states vary in their regulations from none to very strict. In addition to on-site treatment or pickup by a biomedical waste disposal firm for off-site treatment, a mail-back disposal option allows generators of waste to return it to the manufacturer. For instance, waste medicines and equipment can be returned. The waste is shipped through the U.S. postal service. While available in all 50 U.S. states, mail-back medical waste disposal is limited by very strict postal regulations (i.e., collection and shipping containers must be approved by the postal service for use).