What defines an environmentally safe hydraulic fluid?

Timberline Brands LLC provides AW68 hydraulic fluids that are considered biodegradable and suitable for environmentally sensitive environments such as forestry & construction equipment, marine equipment, and off-shore drilling operations. The hydraulics & pneumatics website provides an incredible resource on this subject in its article entitled “Engineering Essentials: Hydraulic Fluids” in the section on ‘Environmental fluids‘.