Environmental health is the branch of public health concerned with all aspects of the natural and built environment affecting human health. In order to effectively control factors that may affect health, the requirements that must be met in order to create a healthy environment must be determined. The major sub-disciplines of environmental health are environmental science, toxicology, environmental epidemiology, and environmental and occupational medicine. Environmental health was defined in a 1989 document by the World Health Organization (WHO) as: Those aspects of human health and disease that are determined by factors in the environment. It is also referred to as the theory and practice of accessing and controlling factors in the environment that can potentially affect health. A 1990 WHO document states that environmental health, as used by the WHO Regional Office for Europe, "includes both the direct pathological effects of chemicals, radiation and some biological agents, and the effects (often indirect) on health and well being of the broad physical, psychological, social and cultural environment, which includes housing, urban development, land use and transport." the WHO website on environmental health states that "Environmental health addresses all the physical, chemical, and biological factors external to a person, and all the related factors impacting behaviours. It encompasses the assessment and control of those environmental factors that can potentially affect health. It is targeted towards preventing disease and creating health-supportive environments. This definition excludes behaviour not related to environment, as well as behaviour related to the social and cultural environment, as well as genetics." The WHO has also defined environmental health services as "those services which implement environmental health policies through monitoring and control activities. They also carry out that role by promoting the improvement of environmental parameters and by encouraging the use of environmentally friendly and healthy technologies and behaviors.