As knowledge improves, so will the procedures. The use of 'zero' as a standard is unhelpful, and should be used sparingly, if at all. This is particularly true where risk assessments are based on default values. Exceeding a standard will not necessarily have fatal or indeed harmful consequences. However, such an occurrence should lead to an investigation of the process performance.
Environmental problems are always complex.
Making changes to environmental policy should always be done with caution, adequate forethought and monitoring of the change. An inappropriate solution to one problem may create a worse problem. Understanding the processes involved is vital. There is a lack of data on environmental fate and its determinant chemical, biological and microbiological processes. Once calculated, standards, of whatever kind, tend to become fixed and immutable.