Volume IV, Number 5
eMDE is a quarterly publication of the Maryland Department of the Environment. It covers articles on current environmental issues and events in the state.
While we may enjoy salt on our fries, and throw salt on our sidewalks to melt snow, certain human activities can increase the amount of salts in waterways to levels that are toxic to aquatic life. The impact of these pollutants is becoming more and more apparent as our population continues to grow, resulting in more sidewalks and highways that need to be salted in inclement weather.
We have known for decades that water quality may not support diverse native biological communities in rivers and streams because of contaminants from human activities. While the Clean Water Act requires supporting aquatic life, since a waterway may be affected by many contaminants, it often isn’t clear which contaminants may be causing the problems.
MDE’s biological stressor identification process objectively determines which contaminants are potential causes of biological impairment throughout the State, and suggests when, for example, both excess salts and excess sediments are present, which contaminant is likely to be causing the problem. Since salts are found naturally, the concentrations are an important factor. Chemical ions, or salts, are found naturally in streams and in varying concentrations across the state. Salts are inorganic; they don’t contain carbon. In water they break up into positively and negatively charged particles called ions. Examples of these ions are chlorides found in table salt, de-icers, and sulfates that have many sources. In Maryland, the major sources of salt concentrations in waterways are mining, wastewater, urban runoff in spring from deicers applied in winter, and some agricultural activities.
MDE is undertaking the complex scientific task of developing standards for toxic ions based on the State’s extensive chemical and biological data. Because many of these salts exist naturally, Maryland may not have existing water quality criteria or Total Maximum Daily Load (TMDLs), because the salts only become toxic in increased concentrations. As a result, MDE has initiated efforts to develop water quality criteria to address excess salts and protect aquatic life. Determining the protective concentration level for specific salts is complex because different organisms have different sensitivities and local conditions may also influence how toxic the contaminants are.
Protective concentrations will have to incorporate three main components to ensure that they are protective of aquatic life, applicable to Maryland conditions, and scientifically defensible. These components are how a substance will be measured, the threshold at which it becomes toxic, and the relationship between that threshold and loss of aquatic life. This approach will produce the most defensible and protective criteria for the protection of aquatic life.
Another consideration in developing these criteria is that Maryland possesses three major ecologic regions - Highlands, Piedmont, and Coastal Plain. As the geology within each eco-region varies, so do the natural characteristics of the surface and groundwaters. Initially the development of toxic ion criteria will focus on the Highland eco-region. Remaining regions will follow a similar approach. The standards, when developed, will provide one more tool to help protect and restore the quality of Maryland’s streams.
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