Biomedical Engineering Reference
In-Depth Information
As with groundwater, the dominant loss mechanism in surface waters is
expected to be biodegradation. Methanol concentrations in the vicinity
of a surface water release would rapidly decrease because of advection
and dispersion particularly in moving surface waters. Owing to meth-
anol's infinite solubility in water, an M100 release in a surface water
body, as discussed in Scenario 2, would disperse to nontoxic levels at a
rate much faster than a release of an equivalent volume of gasoline.
Aquatic toxicity estimates range from a no-observed-effect-concentra-
tion of
29,400mg/l
(Material Safety Data Sheet, 2001). The rate of dispersion is directly
proportional to the amount of turbulent mixing in the aquatic environ-
ment. Tidal flows combined with wind-induced wave action would
cause a large methanol spill to rapidly disperse to levels below toxic
thresholds. The effect of wave action on the speed of contaminant
mixing in surface waters has been measured extensively for gasoline
components following release from recreational vehicles (Malcolm
Pirnie, 1998). In all cases measured, gasoline components quickly
mix throughout the upper layer of the surface water bodies; methanol
is even more soluble in water than most gasoline components and
would, consequently, mix even more rapidly.
To verify these predictions, several computer simulations were
performed to model the advective dispersion of methanol away from
the source area (Machiele, 1989). The first hypothetical simulation
revealed that a 10,000-ton 3 MGmethanol release in the open sea would
reach a concentration of 0.36% within an hour of the spill. The second
hypothetical simulation of a spill at a rate of 10,000 l/h from a coastal
pier exhibited a concentration of
<
1% at the spill site within 2 hours and
to 0.13% within 3 hours after the spill ceased.
23.75mg/l (Kaviraj et al., 2004) to an LC50 of
Biodegradation The dominant process responsible for removal of
methanol in surface water bodies is biodegradation. The reported
half-life of methanol in surface waters under aerobic conditions is
short and has been reported to be as low as 24 hours (Table 2.2) (Howard
et al., 1991).
In flowing water bodies, wind- or current-enhanced mixing typically
maintains dissolved oxygen concentrations sufficiently high to support
