Results of Biological Contamination
Mollusks, in particular, are good indicators of oil pollution because they collect hydrocarbons in their tissues. As a means of assessing the environmental impact of tanker traffic on PWS, NOAA has monitored sediments and mussel beds at eight locations along the tanker route since the Valdez terminal began operating in 1977. Moreover, a baseline study of the port itself began eight years before the terminal and ballast treatment plant opened. Operators of supertankers en route to Valdez fill the cargo tanks with sea water as ballast. At the terminal the tainted ballast water, containing about 1% residual oil from the cargo tanks, is processed at Alyeska's treatment plant by skimming machines, aerators, chemicals, and oil-metabolizing bacteria. After treatment the effluent is pumped into the deep waters of Port Valdez. Since the early 1980's hydrocarbons have been detected in the bottom sediments and in mollusks near the discharge pipe. Subsequently, hydrocarbons have also been found in the bile fluid of certain bottom fish.18
In general, hydrocarbons are not concentrated in the food chain. Yet more than a year after the spill, NOAA biologists have detected elevated concentrations of aromatic hydrocarbons in shellfish such as mussels and clams, suggesting continued uptake of oil from the environment. However, contamination at unsafe levels was only found in two locations, Windy Bay (905 ppb) and Kodiak Harbor (80 ppb), compared to a control site at the village of Angoon (0.02 ppb) outside the spill-impacted area.19
Oil that continues to contaminate mussel beds might be implicated in the failure of the Harlequin duck to breed every year since the oil spill -- Harlequins feed on mussels and clams in shallow waters. An alternative explanation, however, is human interference, which has been aptly described by a scientist working for the Alaska Department of Fish and Game: "Massive amounts of human disturbance to stream mouths and other Harlequin habitats included thousands of mandays of manual cleaning, mechanical tilling, hot-water treatment, Inipol, weir construction, agency and contractor visits, ship and boat traffic in bays and lagoons, and low-level overflights by fixed-wing aircraft and helicopters. Because Harlequin ducks are sensitive to disturbance, and high levels of disturbance can be correlated with poor reproductive performance, this is the alternative hypothesis of the cessation of Harlequin reproduction in the oil spill area of western Prince William Sound."18
In the immediate aftermath of the spill, an estimated 4000 sea otters died from hypothermia induced by the loss of insulation from oil-soaked fur, from emphysema caused by breathing toxic vapors, and from poisoning promoted by oil ingestion. Before the spill approximately 15% of the otters that died each year were mature animals of breeding age. From 1989 through 1991 this figure jumped to greater than 40% but then declined to 22% by 1992, a sign of recovery in the otter population.
More money was spent on rescuing and rehabilitating oiled sea otters than on any other species. One motivation for the rescue plan was to study the disaster's effect on the animals. Otters remain warm as a result of a high metabolic rate; sea lions and seals, on the other hand, have large fat stores for insulation. The proper grooming of a sea otter's fur also provides insulation from air trapped within the interlocking hairs. However, when rescued oiled otters are shampooed, the shampoo remove subaceous oils that made the fur healthy and destroys the insulating ability of the fur. As a consequence, the clean animals shiver uncontrollably in the cold water of holding tanks. To compensate, their metabolic rates rise even higher, some dangerously so. Despite these problems, 225 of the 357 otters saved from the spill zone survived. The nagging question is, would they have survived on their own, in that many of the otters at the treatment centers had been only lightly oiled? Clearly, the effects of captivity were very stressful for the otters. For this otter rescue effort, Exxon spent over $18 million, or $81,000 for each otter that was saved.18
Seabirds are especially susceptible to direct oiling. Estimates range from 10,000 to 100,000 seabirds that perished in the spill. The oil spill arrived just as the breeding guillemot (a small seabird) adults were gathering in "rafts" on the water before heading off to nesting sites. In colonies within the spill site, the populations have been reduced by 40-60% as compared with stable populations outside the spill area. There has also been a dramatic shift in nesting behavior with one severe consequence: an average delay in egg laying of 45 days. One explanation for this anomaly is that the decimation of the guillemot population has deprived them of mature breeding birds to provide proper breeding cues.20
Prior to the Exxon Valdez spill in 1989, the bald eagle population in PWS had rebounded after the banning of DDT in 1972. While the official bald eagle mortality rate from the spill was 151, the majority of carcasses were probably not recovered. Of greater concern, however, was the long-term effect of oil on the surviving eagles and their reproductive potential. Eagles were feeding on oily carrion, and there was concern about bioaccumulation in such birds of prey. Although birds as a group metabolize and excrete crude oil components better than do fish, the heavier hydrocarbons do accumulate in the fat reserves of birds and in the lipid-rich material of eggs. Oiling of the egg shells can be fatal to eight-day-old eagle eggs, but 11-day-old embryos survived shell oiling, suggesting that liver enzymes were sufficiently active three days later in development to neutralize the hydrocarbons. Some scientists have attributed to temporary reduction in eagle reproduction in oiled areas of PWS to the oil spill itself. But the evidence suggests that most eagle reproduction failure during 1990 can be attributed to nest abandonment caused by the disruption of shoreline cleanup, staffed by over 11,000 cleanup workers in 1990.18
Bioassay tests have provided the principal basis for determining crude oil toxicity. In most of the tests mortality has been utilized as the index of toxicity, expressed as LC50 data (the lethal concentration yielding 50% mortality over a specified exposure time). The LC50 data reflect the sensitivity of various marine invertebrates and fish to the "BETX" aromatic hydrocarbons.10 Because LC50 values convey nothing about sublethal effects, however, they are imprecise measures of toxicity.
As a significant portion of the oil has settled into subtidal sediments, there is risk of chronic exposure to fish such as salmon and halibut. Exposure to hydrocarbons can be assessed by analyzing for the presence of the enzyme cytochrome P-450E that catalyzes reactions induced by hydrocarbons. Fish samples from oiled areas have shown markedly high levels of cytochrome P-450E than those from unoiled areas. Whether these results pose a serious threat to the organisms is more difficult to ascertain, but previous studies suggest that elevated levels of P-450E correspond to long-term chronic effects in fish.21 On the other hand, the data indicate little if any detectable aromatic hydrocarbons in salmon samples from PWS.
Fish and marine mammals metabolize most aromatic compounds (ACs) in their livers and then excrete the metabolites into the bile. GC/MS was used to identify AC metabolites (naphthols, phenanthrols, and dibenzothiophenols) in the hydrolyzed bile of a small sample of salmon and pollock caught in PWS several months after the oil spill. The metabolites, which were not found in control fish from unoiled areas, were identified by comparison to those from the hydrolyzed bile of a halibut injected with weathered PBCO. The three types of metabolites were found in abundance in the fish captured in PWS from 5-12 months after the spill. Because PBCO and other North Slope crude oils contain relatively high proportions of dibenzothiophenes as compared to other Alaskan (i.e., Cook Inlet crude) and continental U.S. crude oils, the identification of high concentrations of dibenzothiophenols in the bile of the pollock and salmon implicates the North Slope crude as the source of exposure.22 In subsequent tests performed by NOAA scientists, the levels of bile metabolites in a variety of fish such as pollock and sole diminished to background levels in 1990 and 1991. No sublethal changes or liver lesions were observed in the fish, nor was there any reproductive damage. Because pollock and sole are not bottom dwellers, the earlier high levels of metabolites were tentatively attributed to their diet, which consists of a buffet of smaller fish and crustaceans.18
Because oil is so prevalent in the earth's environment, most vertebrates have adapted to its presence by developing enzymes that degrade oil. Aliphatic hydrocarbons, similar in structure to fatty acids, are metabolized by initial conversion to fatty acids via biochemical oxidation. The toxic "BETX" aromatics, however, react readily with living cells, and the heavier PAH compounds persist in organisms for longer periods by resisting breakdown. While the liver works valiantly to detoxify these chemicals, at some critical threshold the agent can become cancer-causing. After coping with the initial horror of the severe scarring of the natural environment of PWS, concerns about cancer naturally surfaced among the people living in and near Valdez. While most scientists believe that the oil spill will not cause any significant elevation in cancer risk to the human population of PWS, the fears are nonetheless understandable in an era when any increase in quantifiable risk is frightening.
The Impact On Humans. Because many Native Alaskans subsist on wildlife, numerous studies were conducted by NOAA on species normally eaten by them. No hydrocarbon contamination was found in the meat or blubber of harbor seals and sea lions. However, mollusks, such as clams and mussels, had sufficient hydrocarbon contamination to warrant concern. PWS subsistence fishing areas that were obviously oiled were also closed.14
The PWS salmon harvest, which is dominated by the pink salmon, has not been adversely impacted by the spill. In 1990 and 1991, the commercial catch reached all-time records. Because many Alaskans rely heavily on commercial fishing for a livelihood, the strength of the salmon harvest in 1990 and 1991 helped to alleviate fears caused by the drastic curtailment of the 1989 fishing season due to the oil spill. Where commercial fishing was permitted in 1989, the Alaska DEC and the U.S. FDA closely monitored the harvest.
In 1989, local fisherman had been instrumental in using oil containment booms to cordon off three salmon hatcheries and two bays where herring spawn. Every commercial fishery in the path of the oil was affected. Exxon provided monetary compensation to local fishers for lost income. And many fishermen recovered some or all of their losses by leasing their boats and services during the cleanup effort.14
Within six days of the spill, Exxon initiated an extensive water quality sampling program in PWS. The intent of the program was to assess possible impacts on marine species by measuring hydrocarbon concentrations in PWS. Water samples were collected at 35 offshore locations from March through October, 1989. The results of 2300 samples are summarized in Figure 5, a graph of the average PAH concentrations in PWS. The highest PAH concentration was registered in three heavily oiled bays at a level less than 1 ppb, below the 10 ppb maximum concentration of petroleum aromatics allowable by the State of Alaska.19
An interesting anecdote reveals the resiliency of the marine environment. After off-loading of the remaining 1 million gallons of oil that had not spilled from the Exxon Valdez , the vessel was towed to Outside Bay on Naked Island in PWS. Exxon invited NOAA biologists to inspect the blossoming marine life in the cargo holds. The NOAA scientists observed an environment rich in zooplankton, marine worms, algae, bacterial mats, and jellyfish. They theorized that oil-eating bacteria from the nutrient-rich water of PWS had attracted larger predators such as fish, making the damaged hull a microcosm of the marine food chain.18
Figure 5. Average Polycyclic Aromatic Hydrocarbon (PAH) Concentrations for PWS Water
Source: Reference 19, p 27.