Hydraulic fluids encompass a large group of liquids that are
made up of a wide range of chemicals and are typically
produced from crude oil or are manufactured. These fluids are
divided according to their chemical and functional properties;
the three most common are mineral oil-based hydraulic fluids,
polyalphaolefins (PAO), and organophosphate esters.
The main function of hydraulic fluids is to transfer pressure
from one point to another. These chemicals can also serve as
lubricants depending on the specific application. Hydraulic
fluids are used in automobile automatic transmissions, brakes,
and power steering; fork lift trucks; tractors; bulldozers;
industrial machinery; and airplanes.
Isopropylated triphenyl phosphate blend
Hydraulic fluids represent a wide range of products which are
formulated to conform to performance specifications and not to
specific chemical or fate analysis. However, some conclusions
can be made based on what information is available for major
components (e.g., the base oil). Mineral oil hydraulic fluids have
a variable range of carbon number, low water solubility, and
tend to partition to sediments upon release. These oils will
degrade over time and have a low bioaccumulation potential.
There is limited information on the mechanism of toxicity for
hydraulic fluids. They are mixtures of a variety of chemicals,
and some of the effects that are seen may be caused by
additives in the hydraulic fluids. Mineral oil-based and PAO
hydraulic fluids are generally considered not toxic and are
expected to have limited absorption by the lungs, skin, and GI
tract.
Certain organophosphate esters cause neurotoxicity due to
cholinesterase inhibition. Current manufacturing processes for
organophosphate esters used in hydraulic fluids are designed to
minimize the production of toxic isomers such as tri-O-cresyl
phosphate.
