🐠Ecotoxicology Unit 10 – Soil and Wildlife Ecotoxicology

Key Concepts and Definitions

• Ecotoxicology studies the effects of toxicants on ecosystems, including soil and wildlife
• Toxicants are substances that can cause adverse effects on living organisms and ecosystems
• Bioaccumulation occurs when a substance accumulates in an organism faster than it can be metabolized or excreted
• Biomagnification is the increasing concentration of a substance in the tissues of organisms at successively higher levels in a food chain
• Ecological risk assessment evaluates the likelihood of adverse ecological effects from exposure to stressors (pesticides, heavy metals)
• Toxicity testing methods include acute toxicity tests, chronic toxicity tests, and sublethal effects tests
• Soil composition refers to the proportions of sand, silt, clay, and organic matter in a soil sample
• Wildlife ecology focuses on the interactions between wildlife species and their environment, including habitat preferences, diet, and behavior

Soil Composition and Properties

• Soil is composed of mineral particles, organic matter, water, and air
• Soil texture is determined by the relative proportions of sand, silt, and clay particles
  • Sand particles are the largest (0.05-2 mm), followed by silt (0.002-0.05 mm) and clay (<0.002 mm)
• Soil structure refers to the arrangement of soil particles into aggregates, which influences water and air movement
• Soil pH affects the availability of nutrients and the activity of soil microorganisms
  • Most plants prefer a slightly acidic to neutral pH range (6.0-7.5)
• Soil organic matter consists of decomposed plant and animal residues and is essential for soil fertility
• Cation exchange capacity (CEC) is a measure of a soil's ability to hold and exchange positively charged ions (nutrients)
• Soil moisture content influences plant growth, microbial activity, and the fate of toxicants in the soil

Wildlife Ecology Basics

• Wildlife ecology studies the interactions between wildlife species and their environment
• Habitat refers to the natural environment where a species lives and includes food, water, shelter, and space
• Niche describes the role of a species within its ecosystem, including its habitat, diet, and behavior
• Food webs illustrate the feeding relationships among species in an ecosystem
  • Producers (plants), primary consumers (herbivores), secondary consumers (carnivores), and decomposers (bacteria, fungi)
• Population dynamics involve factors that affect the size and growth of wildlife populations, such as birth rates, death rates, and migration
• Carrying capacity is the maximum number of individuals of a species that an ecosystem can support
• Biodiversity refers to the variety of life forms within an ecosystem, including genetic diversity, species diversity, and ecosystem diversity
• Keystone species have a disproportionately large effect on their ecosystem relative to their abundance (wolves in Yellowstone)

Toxicants in Soil and Wildlife Environments

• Toxicants can enter soil and wildlife environments through various pathways, including atmospheric deposition, runoff, and direct application
• Pesticides are commonly used in agriculture to control pests and can persist in soil and accumulate in wildlife
  • Organochlorine pesticides (DDT) are highly persistent and can bioaccumulate in food chains
• Heavy metals (lead, mercury, cadmium) can occur naturally in soil or result from human activities (mining, industrial emissions)
• Polychlorinated biphenyls (PCBs) were widely used in electrical equipment and can persist in the environment for decades
• Polycyclic aromatic hydrocarbons (PAHs) are produced by the incomplete combustion of organic materials (fossil fuels, wood)
• Pharmaceuticals and personal care products (PPCPs) can enter the environment through wastewater discharge and animal feed
• Nanomaterials, such as carbon nanotubes and silver nanoparticles, are emerging contaminants with potential ecological risks
• The fate of toxicants in soil depends on factors such as soil properties, climate, and the chemical characteristics of the toxicant

Bioaccumulation and Biomagnification

• Bioaccumulation is the process by which a substance accumulates in an organism faster than it can be metabolized or excreted
  • Lipophilic substances (PCBs, DDT) tend to bioaccumulate in fatty tissues
• Biomagnification is the increasing concentration of a substance in the tissues of organisms at successively higher levels in a food chain
  • Apex predators (eagles, killer whales) are particularly susceptible to biomagnification
• Bioconcentration factor (BCF) is the ratio of a substance's concentration in an organism to its concentration in the surrounding environment
• Trophic transfer efficiency is the percentage of energy or contaminants transferred from one trophic level to the next
• Bioaccumulation and biomagnification can lead to adverse effects on wildlife health, reproduction, and survival
  • Eggshell thinning in birds of prey due to DDT exposure
• Monitoring programs use sentinel species (mussels, fish) to assess the bioaccumulation of contaminants in ecosystems
• Regulatory measures, such as banning or restricting the use of persistent toxicants, can help mitigate bioaccumulation and biomagnification

Toxicity Testing Methods

• Toxicity testing methods are used to assess the potential adverse effects of substances on living organisms
• Acute toxicity tests measure the short-term effects of a substance on survival, typically over a period of 24-96 hours
  • Lethal concentration 50 (LC50) is the concentration that causes mortality in 50% of the test organisms
• Chronic toxicity tests evaluate the long-term effects of a substance on growth, reproduction, and survival, often lasting weeks or months
• Sublethal effects tests assess the impacts of a substance on physiological, behavioral, or biochemical endpoints (growth rate, enzyme activity)
• In vitro tests use cell cultures or isolated tissues to screen for potential toxicity and reduce the use of live animals
• Standardized test protocols ensure the reproducibility and comparability of toxicity data across laboratories
  • OECD Guidelines for the Testing of Chemicals
• Species sensitivity distributions (SSDs) are used to estimate the range of sensitivities of different species to a toxicant
• Toxicity testing data inform ecological risk assessments and the development of environmental quality guidelines

Ecological Risk Assessment

• Ecological risk assessment is a process that evaluates the likelihood of adverse ecological effects from exposure to stressors
• Problem formulation defines the goals, scope, and endpoints of the assessment and develops a conceptual model
• Exposure assessment characterizes the sources, pathways, and extent of exposure to stressors in the environment
  • Fate and transport models predict the distribution of toxicants in different environmental compartments (soil, water, air)
• Effects assessment evaluates the relationship between stressor levels and ecological responses using dose-response curves
• Risk characterization integrates exposure and effects information to estimate the likelihood and magnitude of adverse ecological effects
• Uncertainty analysis identifies and quantifies the sources of uncertainty in the risk assessment process
• Risk management involves the selection and implementation of actions to reduce or mitigate ecological risks
  • Remediation of contaminated sites, setting environmental quality standards, or restricting the use of harmful substances
• Adaptive management is an iterative approach that incorporates new information and monitoring data to refine risk assessments and management decisions

Case Studies and Real-World Applications

• The Deepwater Horizon oil spill (2010) released millions of barrels of oil into the Gulf of Mexico, impacting marine and coastal ecosystems
  • Ecotoxicological studies assessed the effects of oil and dispersants on various species (fish, shrimp, corals)
• The Chernobyl nuclear accident (1986) contaminated large areas of Europe with radioactive fallout, affecting wildlife and soil
  • Long-term studies have investigated the bioaccumulation of radionuclides in plants and animals and the ecological consequences of chronic radiation exposure
• The use of neonicotinoid insecticides has been linked to the decline of pollinator populations, particularly honey bees
  • Toxicity studies have demonstrated the sublethal effects of neonicotinoids on bee behavior, learning, and colony health
• The Minamata Bay mercury poisoning incident in Japan (1950s-1960s) resulted from the release of methylmercury by a chemical factory
  • Methylmercury biomagnified in the marine food chain, causing severe neurological disorders in humans who consumed contaminated fish
• The use of lead shot for hunting waterfowl has led to the ingestion of lead pellets by birds, causing lead poisoning and mortality
  • Regulations banning the use of lead shot have been implemented in many countries to protect waterfowl populations
• The Elk River chemical spill (2014) in West Virginia released a coal-processing chemical (MCHM) into the water supply, affecting aquatic life and human health
  • Toxicity studies were conducted to assess the effects of MCHM on various aquatic species and to inform drinking water safety guidelines
• The Flint water crisis (2014-2019) in Michigan exposed residents to elevated levels of lead in drinking water due to a change in water source and inadequate treatment
  • Ecotoxicological studies investigated the impacts of lead on aquatic ecosystems and the potential for bioaccumulation in the food chain