MAINE ENVIRONMENTAL PRIORITIES PROJECT
ISSUE: TOXIC CONTAMINATION OF COASTAL WATERS
by: John Sowles
Maine Department of Environmental Protection
Introduction
Toxic contaminants are chemicals that have the potential to harm living organisms. Whether a contaminant actually induces toxicity depends on several factors including concentration, chemical form, availability, and target biological system. Presence of toxic contaminants in the environment or even tissues does not necessarily signify toxicity. For example, at low concentrations, copper is a micronutrient essential to the photosynthetic electron transport system yet at higher concentrations is marketed as an effective herbicide. The form of mercury influences its toxicity. Methylated mercury is much more toxic than inorganic mercury (Mitra, 1986). Bio-chemical transformations can change benign chemicals to toxic forms and within food chains toxic chemicals at non-toxic concentrations are bioconcentrated to toxic levels. Furthermore, in association with other chemicals, non-toxic chemicals may become toxic.
Impacted Resources
All marine and estuarine life is susceptible to toxic contamination. Plants are generally directly affected through their medium. In the case of phytoplankton, this is water, and in the cases of attached plants, (e.g. eelgrass and epibenthic algae), water and substrate. Animal life is affected through contact with both their medium as well as food items.
While ecological and biological losses are the subject of this paper, one might also be aware of the economic implications of toxic contamination. Lesions, tumors and general market appearance leads to lost consumer demand. At extremes, even the perception of toxic contamination, regardless of its concentration or whether or not there is likely an effect, can drive an uninformed public to unreasonable actions.
Agents
The list of chemicals and chemical complexes is too large to discuss each contaminant separately. I have therefore elected to briefly discuss heavy metals, organics, and chlorine. These classes of contaminants most threaten marine life due to a combination of toxicity, frequency of use, affinity to bioaccumulate and/or persistence.
Metals are naturally occurring elements in rocks and minerals. Over time, metals are leached out of rocks and soil into the environment. The natural accumulation of metals in the estuaries and coastal waters has been accelerated by humans through such activities as soil disturbance, mining, manufacturing, urbanization, burning fossil fuels and using manufactured products such as paints, pesticides, sacrificial anodes, and antifoulants (Ketchum, 1972). Heavy metals are considered the most toxic of the metals and include those that are essential to biological process (e.g. Cu, Cr, Ni, Zn) and those that are non-essential (e.g. Cd, Hg, Pb). Non-essential heavy metals are the most toxic.
Organic compounds include both naturally occurring and manufactured chemicals. As with metals, human activity has greatly increased the amounts present in today's environment. Of the petroleum hydrocarbons, polycyclic aromatic hydrocarbons (PAHs) are the chemical species within petroleum that are most frequently discussed in terms of toxicity. Impacts from oil spills are discussed in a separate issue paper (Sowles, 1995a). PAHs derive from raw petroleum products and the combustion of wood, coal, and petroleum. Sixteen PAHs are on EPA's priority pollutant list due to their toxicity. High molecular weight PAHs are less acutely toxic but more carcinogenic and teratogenic than low molecular weight PAHs. Furthermore, high molecular weight PAHs degrade more slowly and therefore accumulate in sediments.
Organo-tins are very effective compounds used to control marine fouling. They are also known to be extremely toxic to marine life (Hall and Pinkney, 1985). Although now regulated, TBT continues to be widely used on large commercial and military vessels.
Halogenated organics (esp. the brominated and chlorinated) are considered toxic due to their carcinogenicity and affect on vertebrate reproductive systems. DDT, chlordane, and heptachlor and industrial cousins such as polychlorinated biphenyls (PCBs) are examples of chlorinated insecticides and compounds that were responsible for the decline of raptors in the mid-1900s. Dioxins and furans, also in this class, are byproducts of both natural (Grass, 1994) and industrial processes involving heat, chlorine and pressures. Most of the halogenated compounds are efficiently bio-concentrated.
Chlorine deserves separate mention due to its wide use to disinfect wastewater. Unlike the above classes that are of concern mainly because of their toxicity after accumulating in sediments or food chains, chlorine is toxic in the water column. (Note that two other chemicals, ammonia and nitrates may also be toxic in the water column. They have been discussed in the nutrient issue paper (Sowles, 1995b)).
In general, marine species are more sensitive to chlorine than freshwater species (U.S. EPA, 1983). Beyond lethal effect, chlorine compounds also cause avoidance behavior in fish (Middaugh, et al. 1977) thus potentially affecting spawning runs. No studies in Maine are known to have addressed this difficult question. Because the analytical detection limit is above that which is detectable by marine life, it is difficult to demonstrate cause and effect under ambient conditions. In addition to municipal wastewater treatment plants, residential septic systems and food processing facilities are the dominant sources.
Sources and Pathways
Like other pollutants, toxic contaminants enter Maine's coastal waters via rivers, atmospheric deposition, direct discharges, and occasionally groundwater.
Point Sources
Licensed municipal and industrial treatment plants represent a large source of toxics to Maine waters. Whether these point sources are the largest source is not known since no comprehensive estimate of mass loading has been conducted that assesses relative contributions from point, non-point, natural and atmospheric sources. While relatively few discharges enter the coast directly, most eventually enter coastal waters as they flow down rivers. Commonly discharged toxic contaminants are listed by industry in Table 1.
Table 1
Numbers and types of discharges to Maine waters. Contaminants listed are "selectively " discharged depending on industrial process.
Industry Type Number in Maine Contaminants
Tanneries 2 Cr, Hg, Zn, hydrocarbons
Metal Finishing/Electronics 7 Cr, Cu, Pb, Hg, Zn, hydrocarbons
Pulp and Paper 17 Cr, Cu, Pb, Hg, Zn, dioxins
Textile 11 Cr, Cu, Pb, Hg, Zn, hydrocarbons
Chemical Products 6 As, Cr, Cu, Pb, Hg, Zn, hydrocarbons
Municipal Sewage 100+ all of the above, PAHs, pesticides, others
Source: Doggett and Sowles, 1989
Individual citizens also share in the release of toxic contaminant to coastal waters. With over 80% of the state population living within 50 miles of the coast, there are over 100 municipal sewage treatment plants in Maine's coastal watersheds. Half of these discharge directly into marine or estuarine waters while the other half discharge to rivers that run to the sea. In addition, about 3000 homeowners discharge directly to the coast. In 1987, the Legislature prohibited construction of new overboard discharge systems. Toxic discharges from these systems consist of chlorine.
Toxic contamination from domestic waste in Maine is not known. However we do know that the improper disposal of household hazardous waste can be a problem. Without facilities and incentive to recycle old pesticides, cleaners and solvents, one may assume that some risk is posed by uninformed or careless individuals.
Non-Point Sources
Stormwater runoff contains a multitude of toxic chemicals derived locally and from great distances. Paved and other impervious surfaces collect spills, leaks and atmospheric deposition. With urbanization, homeowners appear to be increasingly using "Weed and Feed" herbicides. That, combined with the large amount of impervious surfaces (e.g. parking lots and roads) in urban areas, makes pesticides vulnerable to washing into streams, rivers and estuaries.
Based on studies done in Penobscot and Casco Bays by Johnson et al. (1983) and Larsen and Doggett (1988) stormwater and other unregulated discharges appear to be significant sources of metals, PAHs and PCBs to Maine's coastal environment. PCBs were used in electrical equipment such as transformers and capacitors. Much of the electrical equipment is still in use. Sources of PCB contamination today is not known.
Recreational boating contributes oily wastes, bottom paints and disinfectants used in onboard toilets. Indirect effects related to boating activities include runoff from boat yards and marinas of oily wastes and/or bottom paints.
Sediments may also be sources of toxic contaminants that have accumulated over many years. Where fresh river water meets saline coastal water, most dissolved metals and organic acids attach to particles and settle to the bottom. Thus, in the coastal zone, many pollutants accumulate in sediments rather than being diluted by the ocean. Figure 1 clearly demonstrates this phenomenon for PAHs in Penobscot Bay. During spring runoff, floods, and storms, sediments and metals are transported and redistributed farther out into the estuary and bay where they become available to bottom-dwelling animals. Dredging, storms and currents can resuspend or expose these materials thus reintroducing them into the food web.
Figure 1
The distribution of total PAH concentrations in surficial sediments of Penobscot Bay
Source: Johnson et al., 1993
Exposure
Virtually the entire coast of Maine is exposed to toxic contamination because of circulation patterns and atmospheric deposition. However, certain geographic areas are more exposed than others and include mouths of industrial rivers, commercial ports, waters adjacent to dense human development and waters adjacent to metal mines. Other areas, while not necessarily exposed to more toxic loading, are more vulnerable due to the physical characteristics of the waterbody. Areas that are poorly flushed and deposit sediments tend to retain toxic contaminants associated with particles.
Nature of Potential Impact
Toxicity operates at many levels of biological organization from the bio-chemical through species to the ecosytem. Mechanisms of toxicity vary from simple poisoning, induction of cancer, genetic mutation through behavioral effects. Ultimately, toxicity depends on the sensitivity of each individual organism. Most organisms have evolved ways to cope with a certain amount of toxic materials (e.g. hepatopancreas in lobsters and liver in vertebrates) with some organisms better adapted than others.
Many toxic effects are transferred through the food chain. Long lived predators (including marine mammals, billfishes and humans) are efficient accumulators of toxic contaminants. This is because in addition to contact with water and substrates, they consume other plants and animals that may have accumulated contaminants.
Beyond acutely lethal effects, effects of toxic contaminants become more complicated and less obvious. Low levels of toxic contamination, while perhaps not poisonous, can produce more subtle sub-lethal secondary effects including a predisposition to disease, loss of vigor, and behavioral changes that affect reproduction, ability to compete and ultimately survival. These sub-lethal effects, combined with other stressors can impact populations and entire ecosytem dynamics.
Bottom dwelling animals living in intertidal and shallow coastal waters are the base of the food chain for shorebirds as they migrate to and from northern breeding areas and southern wintering areas. Local waterfowl are dependent on these benthos during the winter as well. Maine's larger predatory marine fish, the same ones sought by the commercial fishery, are ultimately entirely dependent on benthos for food. Contaminant build up in the sediments and bottom dwelling animals can therefore be both ecologically and economically detrimental.
It would seem, therefore that the best strategy for protecting marine life is through managing toxics to protect both the lower and upper trophic levels. The base of the food web, phytoplankton, zooplankton and bacteria, appear to be very sensitive and long lived predators may magnify apparently innocuous low concentrations of toxics to significant levels.
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