health and safety plan solid waste management unit assessment

HYDRAULIC FLUID 68-21
molecular weight (more liquid) const.ituents would tend to volatilize
first, the remaining material would generally have lower volatilities
and lower water solubilities.
68.2.2 Transformation Processes in Soil/Ground-water Systems
An assessment of environmental persistence for hydraulic fluids is
difficult given the variety of materials involved and the lack of
pertinent data. Thus, most of the statements given below are both
general and speculative in nature. Only the phosphate esters have been
the subject of several environmental studies (see Chapter 49 of this
Guide and references 1490 and 1496).
Hydraulic fluid oils are expected to be moderately persistent in
the soil/ground-water environment because of their resistance to hydrolysis,
oxidation and biodegradation. The general resistance to
hydrolysis (for saturated and unsaturated hydrocarbons) is described by
Harris (529). However, the organic esters, phosphate esters and
polyglycols would be somewhat more susceptible to hydrolysis, especially
under basic conditions.
The assessment of the resistance to biodegradation is more com-
.plex. Most of the molecules are so large that passage through cell
walls (where metabolism or degradation is relatively easy) is hindered
and much of the biodegradation must be carried out by extracellular
enzymes secreted by the microbes. Such difficulties aside, many
studies on petroleum hydrocarbon materials (oils as well as light
distillates) have showed moderate to high eventual susceptibility to
biodegradation for the bulk of the material (1842). A period of microbial
adaptation may be required. The organic esters, phosphate esters
and polyglycols would be expected to be more readily biodegraded.
Different constituents of the oil will differ significantly in
their biodegradability for reasons related to molecular size, structure
and toxicity. For example, highly branched alkanes are much less
biodegradable than linear alkanes, and polycyclic aromatic hydrocarbons
with three or more rings are very resistant to biodegradation (515).
For all hydrocarbons, aerobic biodegradation would be expected to be
much more important than anaerobic biodegradation (1841). Because of
this, and because of the decrease in microbiological activity with
increasing soil depth, oil constitutents reaching deep anaerobic soils
could persist for very long time periods.
68.2.3 Primary Routes of Exposure from Soil/Ground-water Systems
The above discussion of fate pathways suggests that the components
of hydraulic fluids will vary widely in their volatility, tendency to
sorb to soil, and potential for bioaccumulation. However, the base
stock of hydraulic fluids manufactured with mineral oils are expected
to be very strongly sorbed to soil because of their high molecular.
weight and low water solubility. These compounds have extremely low
volatility in pure form, but when present in water may have relatively
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