Risk assessment beginning at 1980s has developed greatly in content, scale and methods of assessment from one chemical and one receptor to its current application at large spatial and temporal scales in the 20 years. In the 1980s, the main assessment content was from toxicity of one chemical to human health risk. In the 1990s, risk assessment as a management tool had to be applied to populations, communities, and eventually to the ecological landscape at large scales. The risk analysis of multiple stressors, not just multiple chemicals but multiple types of agents, was also taken into account. During the late part of 1990s and early 2000s, the ecological risk assessment was broadening to include not only chemicals and ecological affairs but also a wide variety stressors, such as the impacts of human activities(urbanization, land use and land cover change, fishery and climate change, etc.) and the assessment scale was expanding to region and landscape scales.
Frameworks and statistical models are the key of regional ecological risk assessment. The risk assessment framework presented in the National Research Council(NRC) Red Book played a key role in the development of ecological risk assessment. After years of modification, the assessment framework had been improved to be perfect till 1998. The Environmental Protection Agency(EPA) framework proposed an integrated framework that covered both human health and ecological risk assessment including a detailed description of the process and showing how the process could be applied to a broad range of situations. Since then, various ERA framework have been developed for use in some countries(e.g. Netherlands, Australia, United Kingdom) and for specific situations. The statistical methods are the quantitative methods of ecological risk assessment. For one chemical stressor, the ratio value model and exposure-response model are adopted, but for the multiplestressors, multiple receptors, large scale of complex regional landscape, the methods aren’t suitable because many uncertainties will appear during the extending from one stressor small scale to multiple stressors large scale. In the regional ecological risk assessment, Relative Risk Assessment(RRA) based on weight-of-evidence(WOE) are used widely. WOE approaches reported in the literature vary broadly from subjective and qualitative to quantitative and the categories of which include qualitative combination, expert ranking, consensus ranking, semi-quantitative ranking and sediment quality triad. WOE approaches could be used in retrospect assessment, causation assessment and the whole process of ecological risk assessment.
In the future, as a universal framework for ecological management, ecological risk assessment should develop deeply in resolving the problems of scale extending, uncertainty and assessment standard. At the background of global ecological crisis, regional ecological risk assessment will emphasized the fields and aspects in close relationship with global changes, such as human activities, geological disasters and climate affairs and ecological risk resulting from policy error and ecology safety, etc. Regional ecological risk assessment has the potential of becoming quantitative tools of management decision if it integrated with economy, society and culture