Page 17 - Environmental Control in Petroleum Engineering

6 Environmental Control in Petroleum Engineering

salt affects the ability of plants to absorb water and nutrients from soil.
It can also alter the mechanical structure of the soil, which disrupts
the transport of air and water to root systems. Water with dissolved
salt concentrations below about 2,500 mg/1 have minimal impact on
most plants (Deuel, 1990). LC 50 values for dissolved salt concen-
trations for freshwater organisms are on the order of 1,000 ppm.
(Mount et al., 1993).
The toxicity of drilling muds varies considerably, depending on
their composition. Toxicities (LC 50) of water-based muds containing
small percentages of hydrocarbons can be a few thousand ppm. The
LC 50s of polymer muds, however, can exceed one million, which
means that fewer than 50% of a test species will have died during
the test period.
The toxicity of heavy metals found in the upstream petroleum
industry varies widely. The toxicity of many heavy metals lies in their
interference with the action of enzymes, which limits or stops normal
biochemical processes in cells. General effects include damage to the
liver, kidney, or reproductive, blood forming, or nervous systems. With
some metals, these effects may also include mutations or tumors,
Heavy metal concentrations allowed in drinking water vary for each
metal, but are generally below about 0.01 mg/L. The heavy metals in
offshore drilling fluid discharges normally combine quickly with the
naturally abundant sulfates in seawater to form insoluble sulfates and
precipitates that settle to the sea floor. This process renders the heavy
metals inaccessible for bioaccumulation or consumption.
Nuclear radiation from NORM can disrupt cellular chemistry and
alter the genetic structure of cells. In most cases, however, radiation
exposure from NORM is significantly lower than that from other
natural and man-made sources of radiation and does not represent a
serious health hazard (Snavely, 1989).
The various chemicals used during production activities can also
affect the environment. Their toxicities vary considerably, from highly
toxic to essentially nontoxic. In most cases, however, the concen-
trations of chemicals actually encountered in the field are below toxic
levels (Hudgins, 1992).
The primary environmental consequences of air pollutants are
respiratory difficulties in humans and animals, damage to vegetation,
and soil acidification. Releases of hydrogen sulfide, of course, can be
fatal to those exposed.