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L&W Home > Monitoring & Assessment > A Decade of Toxic Monitoring Along Maine's Coast > Introduction & Methods

Introduction & Methods

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Introduction

Contamination of our environment by toxic chemicals is a serious global concern. By the early 1960s, the public was well aware of the unintended consequences of widespread chemical use. In Minimata Japan, over one hundred people had been tragically poisoned after consuming mercury contaminated fish. Here in the United States, wildlife including the American bald eagle and peregrine falcon were nearly extirpated by pesticides, most notably the persistent organochlorine compounds like DDT. In Maine, human health advisories exist (DHS link here) warning people of the risk of eating sportfish caught from freshwater. On the coast, an advisory warns against eating tomalley or eating large striped bass and bluefish. (for more on toxic contamination in Maine Coastal Waters see MEPP link).

Interpreting toxic contaminant data is not simply a matter of detecting a toxic chemical. With today’s advanced laboratory techniques, we are able to detect toxic contaminants in virtually any sample we collect, whether or not they cause toxic effects. Because many toxic contaminants are naturally occurring (eg. all metals and many hydrocarbons), we invariably detect them. Chemicals known to be toxic at higher concentrations are frequently the very same chemicals required for normal cellular functions, but at lower concentrations.

Hundreds of new chemicals are being developed and placed on the market each year. The ubiquitous nature of pesticides, chemical products and byproducts of our technological society presents a continuing challenge to environmental and human health management. Even though some chemicals have been banned from use in the United States, they enter the U.S. on currents of air and water, food products, commerce and waste from other countries where they are still used. Monitoring their presence in our environment is a key step in assessing and managing the threat from toxic contamination.

Objectives

In the late 1980s, we initiated a project to assess the levels and locations of toxic contaminants along the coast.

The project’s immediate goals were

1. to gather sufficient information to enable us to define "normal" environmental levels of certain toxic chemicals,

2. to determine whether levels pose an unacceptable risk to humans and/or coastal marine life, and

3. to be able to discriminate between natural sources and human sources.

Maine Mussel Watch

The common blue mussel, Mytilus edulis, was selected as our primary tool to assess Maine’s coastal water quality. Mussels have been successfully used around the region and world. The large data sets from these other programs (NOAA & Gulfwatch) provide us a context to assess conditions in Maine. Sampling mussels has an advantage over directly sampling seawater in that they filter large volumes of water each day and accumulate contaminants that may not otherwise be detected in the water. Also, water samples represent conditions at the exact time when the water was sampled. Mussels integrate conditions over weeks and months. Mussels are sedentary and therefore reflect local conditions making them suitable for detecting sources of contamination. They occur along the entire coast and are relatively easy to collect. Mussels have an advantage over sediment since they reflect levels of contaminants that are biologically available. And finally, as a food with considerable health benefits to people, by incorporating them into our monitoring program, the public is assured that the areas open to harvest are safe. (For more on the human health, see section below entitled human health implications.)

Station Selection Considerations

Stations are selected based on five primary factors.

1. Reference Conditions - Since many pollutants are naturally occurring elements and compounds, their presence does not necessarily signify pollution. Understanding the natural concentrations and variability in biota is critical to interpreting monitoring data. Therefore, inclusion of stations along the coast which are located in areas thought to be free of "pollution" is essential to this program. Although the coast of Maine is not entirely pristine, there remain areas that have been spared the impacts associated with either present day or historical industrial or commercial development. These "reference" areas are in relatively remote sections of the coast where anthropogenic contamination is thought to be minimal. Data from the reference stations are used to describe normal background levels which in turn forms the basis on which the other stations are evaluated.

2. Sources of pollution - In areas where contamination is known to have occurred, stations have been established to assess the severity of contamination. Through monitoring these stations over time and comparing them to the reference stations, trends may develop that help evaluate whether environmental management practices are working.

3. Spatial distribution - Because Maine's coast covers a large geographic area and includes many different environments, stations have been distributed throughout the coast.

4. Physiography and hydrography - Maine's coast is highly variable ranging from bold deep water rocky habitats to shallow mud flats in enclosed embayments. Human activity and natural processes affect water quality in very different ways depending on flushing, bottom sediment type, land and water use. Stations have been placed in areas with an assortment of these conditions.

5. Add-on opportunities - Stations are also located on a case by case basis if they address a specific question or there is the potential to compliment work being done elsewhere. Damage assessment after a chemical spill, evaluating shellfish beds, and research into contaminant uptake kinetics are a few examples.

Secondary considerations for station selection include accessibility, condition of mussel population, turbidity from resuspended sediment, and public interest.

Sample Collection

Contaminant body burdens vary with season, age, location in the intertidal zone and reproductive state. Effort was therefore made to standardize these variables so that comparisons between years and locations may be made. Collection is done during an index period that begins at the end of August and continues through early October.

Samples are collected from the low intertidal or shallow sub tidal zone. Mussels are between 50-60mm long. The area of collection is both located and sized to reflect the waterbody of interest. In most cases the area is about 100 to 200 meters long.

Region Descriptions

We have divided the coast into eight regions to collect data that is representative of the various environmental conditions encountered in Maine (Figure 1). Each region roughly reflects an ecological system such as a large estuary or type of coastline or tidal regime. Following the region name is a two letter code that facilitates querying the data.

The Piscataqua Estuary (PQ) is at the southwestern corner of Maine. This is a true estuary that drains southern Maine and New Hampshire. The area has a long and rich industrial history.

The South Coastal (SC) region is mostly sand beach and salt marsh with a straight coastline. Several small rivers drain into this region.

Casco Bay (CB) is a semi-enclosed system and has a deeply indented coastline with many islands. About a quarter of Maine’s population lives in this bay’s watershed. The western part of the bay is well developed and industrialized while the eastern part has relatively light development.

The Mid Coast (MC) region is also indented but is more open to the ocean. It too, contains a mixture of light development and industry.

Penobscot Bay (PB) is the drowned valley of the Penobscot River. At the head, the river drains the central part of Maine. On the river itself are several large cities. Industry includes pulp and paper and petrochemical facilities. The bay contains several large island communities. Land-use in the areas is widely varied from urban to forest.

Blue Hill-Frenchmans Bay (BF) is generally light to moderately developed. Exceptions include two metal mines. Acadia National Park lies in the center of Frenchman’s Bay.

The East Coast (EC) region is a bold coast with several small rivers draining to it. Development is generally light with small towns interspersed along its length.

Passamoquoddy Bay (PB) is semi-enclosed with tides in excess of 20 feet. Cold, nutrient rich waters make this area one of the most productive areas on the Maine coast. The bay supports a large concentration of salmon aquaculture operations. Industrial development in this part of Maine is light.

Station Coding

The underlying mussel database uses a 6 letter code to easily identify stations. The first 2 letters refer to one of the 8 regions discussed above. Within each region, stations are coded with 4 letters following the regional 2 letter code. For example, CBFROF is the Casco Bay region, Fore River, Outer Fore River segment. Table 1 contains the names, towns, and codes of all the stations for which we have data.

Definition of Normal Baseline

To define what we consider to be the normal range of concentrations for each contaminant, we used values from 24 reference stations. Since the data from those stations fit a normal distribution, we were able to take the arithmetic mean and its standard deviation to describe the population. For the purposes of this program, "normal" concentrations for each contaminant was arbitrarily defined as plus and minus 2 standard deviations around the mean of concentrations found in mussels collected at the reference stations (+/-2s). Values outside this range are considered anomalous, although not necessarily a sign of pollution, and are presented in Table 2.

Percent Deviation above the Norm was calculated using the following formula:

% Dev. = (((Cs/Cb)-1) *100) +100

where

% Dev. = Percent Deviation above the Normal Range

Cs = Sample Concentration

Cb = Upper Limit of Normal Range

How to Read Station Summaries

We assumed that most people are interested in their particular waterbody and less interested in the contaminant itself and have therefore produced reports that discuss conditions at the station that shows which, if any, contaminants warrant attention. On a single graph, we present results for several contaminants in relation to the State of Maine "background."

The chart shows where samples were collected. Two formats are used. The more common format is the cross hatched area that shows the area over which mussels were collected. Less common, is the black triangle, the point of which indicates a small feature such as a ledge, on the chart.

The narrative follows the chart. It is divided up into at least three paragraphs describing the physical features of the site and access considerations, land-use activity in the immediate area and potential sources of contamination, and finally an interpretation of the results.

The graph requires a bit of explanation. A single horizontal line lies about 1/3rd the way up on the graph at 0 on the y-axis. This line is the upper limit of what we consider within the normal baseline range for Maine. Bars exceeding the line are above normal and warrant further investigation. The degree to which the bar exceeds the line is expressed as a percentage above the upper limit of the Maine "baseline." At a glance, then, one can see which, if any, contaminants at a location is higher than what we consider normal. Bars ending below that line indicate that concentrations of that particular contaminant are within what we consider to be normal for uncontaminated areas of the Maine coast.

Raw data are presented in a table below the graph. This may come in useful for those people interested in using these data or comparing these data with data from other programs. Individual replicates are presented so variability may be assessed if desired.

Human Health Implications

The objective of our monitoring is to assess environmental health. However, by reporting test results on popular seafood products, we risk discouraging readers from eating seafood when most nutritionists and medical professionals recommend a varied diet that includes fish and seafood. Seafood is low in fats and cholesterol, is rich in minerals and vitamins, and contains the beneficial omega-3-fatty acids. Several studies have shown that including seafood in the diet is associated with a lower incidence of heart disease. For more on the health benefits of seafood and seafood safety see http://www.ocean.udel.edu/mas/seafood/nutritioninfo.html

Whether or not levels of toxic contaminants are in the "normal" range is generally unrelated to human health. "Normal" levels or some chemicals can be toxic while conversely elevated levels of some contaminants may not be toxic. Human health risk assessment uses a different method from that used to assess environmental contamination.

Interim Shellfish Action Levels to protect human health (Table 3) have been developed by the State Toxicologist at the Maine Bureau of Health. Mercury and lead are the only two metals found to exceed their human health action level and then only at a few stations. Where concentrations are at or above any of these levels, it is noted in the narrative interpretation of that station’s results. Interim Shellfish Action Levels are based on wet (live) weights and are not directly comparable to the dry weight values reported in this document. To convert the dry weight data to wet weights, dry weight is multiplied by percent solids.

A Note of Caution Regarding Data Interpretation

An accepted feature of all sample results is variability. For many reasons, separate samples from the same areas yield slightly different results. Although we try to eliminate as many of these reasons through standardization, replication, quality assurance and quality control measures, some are impractical if not impossible to eliminate. For example, mussels across the state and even at a given site are genetically different with different growth rates, accumulation rates, etc. Even in the laboratory, analyses conducted on different days are slightly different due to varying performance of equipment and staff. Variability introduces uncertainty to the measurement making it difficult to detect trends over time and differences between geographic areas.

Reducing variability costs money. Balancing costs with the degree of confidence necessary to answer this program’s objectives was confronted early on. We elected to sacrifice "confidence" in favor of gathering information on more areas of the coast as a first step. Many of the early data represent single samples. These should be considered as screening data only and are often adequate to provide a basis for additional monitoring. Results from single samples, however, are not to be used to make management decisions because of the uncertainty of what they represent.

When comparing these data with data collected by others, be careful to assure that the measurement units are the same. Samples reported here are generally on a dry weight basis. Other programs may report data on a wet weight basis. Sample collection protocols, sample preparation, analysis, detection limits and data summarization techniques influence results.