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The Impact of Drilling and Production Operations 127

soiling or chemical deterioration of surfaces. For plants, the impact
includes damage to chlorophyl and a disruption of photosynthesis. Sulfur
dioxide can also accumulate in soils, lowering the pH and modifying the
soil nutrient balance. The impact of air pollutants on humans and animals
includes irritation and damage to respiratory systems.
The impact of sulfur dioxide and hydrocarbons (ethene) has been
observed on plants at concentrations as low as 0.03 ppm and 0.05 ppm,
respectively. Sulfur dioxide concentrations on the order of 1 ppm can
cause constriction of airways in the respiratory tracts of humans
(Seinfeld, 1986).

3.10 ACOUSTIC IMPACTS

Some of the operations associated with drilling and production
can generate high noise (acoustic) levels. The impact of these
noises, however, is normally small. The most important sources are
the seismic operations used during exploration. A number of studies
have been conducted on ways to minimize the environmental impact
of these operations (Ruiz Soza, 1991; Wren, 1991; Wright, 1991;
Bertherin, 1991).
An extensive review of the acoustic impact of drilling and produc-
tion on marine mammals was conducted by the American Petroleum
Institute (1989a). This review concluded that acoustic impacts from
offshore petroleum operations, including sounds from ships, aircraft,
seismic exploration, drilling, dredging, and production, are limited
primarily to short-term responses by mammals. For example, an
airplane flyby can cause pinnipeds (seals and walruses) to jump into
the water, abandoning their young. No long-term impacts on marine
mammal populations have been observed, however. Explosives can
injure mammals in water within a few hundred meters, but seismic
air guns are not believed to be physically harmful unless the animals
are very close to the guns.
The effects of air guns on fish with swim bladders, e.g., anchovies,
was also studied (American Petroleum Institute, 1987b). The overall
effects of seismic surveys using air guns appears very small. Notice-
able effects on eggs and larvae would only result from large numbers
of multiple exposures to full seismic arrays. The largest reduction in
survival rate (35%) was for four-day-old larvae exposed 3-4 times to
air guns passing overhead at a distance of 10 feet. Seismic pulses with
air guns appear to have a lethal radius for fish of about 1-2 meters.