This section is authored by Dr. Gretchen Bielmyer-Fraser, Associate Professor in the Chemistry department at Jacksonville University.
Contaminants are chemicals that are found at elevated concentrations in any environment. Some are produced solely by human activity, but many are also produced naturally in small quantities. Both anthropogenic (human-made) and naturally occurring compounds may become contaminants when they are introduced into ecosystems at elevated concentrations, often as a result of human activity (examples are polyaromatic hydrocarbons, or PAHs, and metals). Concentrations of naturally-occurring compounds often vary with local geology and environment. Thus, it is more difficult to detect human input and harmful concentrations for naturally occurring compounds than for those that are produced solely by human activity.
A chemical becomes environmentally significant when it is prevalent, persistent, and toxic. The prevalence of a chemical in any system depends on how much of it goes in and how quickly it goes out, either by flowing out or by degrading. A compound that is persistent breaks down slowly and is removed slowly. The probability of long-term toxic effects increases with persistence. Some types of chemicals are taken up and stored in tissues of plants and animals with little or no degradation, i.e., they bioaccumulate. Bioaccumulated chemicals are stored in tissues of prey organisms and when prey are eaten, the chemicals can be transferred to predators and travel up the food chain in increasingly higher levels, i.e., they biomagnify. Thus, organisms containing bioaccumulated chemicals can act as a reservoir to various degrees.
Contaminants can also reside in sediments and in the water. They will partition between biota, sediments and water in ratios that depend on the chemical and the environmental conditions. The sediments of rivers often serve as reservoirs for chemical contaminants. Many of the environmentally important compounds are attracted to the organic matter in sediments and end up there, regardless of how they enter the water body. Plants and animals that live in sediments (benthic organisms) are potentially exposed to contaminated water and sediments, so assessments of their toxic responses to contaminants are particularly important in determining overall river health. Additionally, any activity that disrupts the sediment (i.e. dredging) can potentially remobilize contaminants into the water column.
5.1.1. Assessments of Status and Trends
Chemicals in four environmentally significant categories are evaluated in this report. The categories include 1) polyaromatic hydrocarbons (PAHs), 2) metals, 3) polychlorinated biphenyls (PCBs), and 4) pesticides. These chemicals vary in their chemical structure, their sources, and their specific fates and effects, but they all have a high potential for prevalence, persistence, toxicity and bioaccumulation. Each of the categories is discussed separately.
Sediment contaminants are examined in terms of frequency of occurrence, the concentrations present, and whether any trends up or down exist. The relative toxic impact of the different classes in different regions of the LSJR was estimated.
Water column concentrations of metals are included because more of these compounds will reside in the water column than the other classes of chemicals. Water column concentrations of pesticides have also been included because they will be distributed in the water column to some degree, depending on solubility, volatility and other characteristics.
The rate at which chemicals are released into the environment clearly affects their potential environmental impact. In addition to examining concentrations of contaminants found in the LSJR sediments and water, we examined the status and trends of reported chemical releases into the atmosphere and waterways of the LSJR using the Toxics Release Inventory database (EPA 2015c; EPA 2015b) and the Risk Screening Environmental Indicators model (EPA 2013c), both provided by EPA. Releases of all chemicals are discussed in Section 5.4 and releases of the metals and PAHs are discussed in their respective sections.