8.4 Terrestrial toxicology
10 min read•august 20, 2024
Terrestrial toxicology examines how toxic substances affect land-based ecosystems, including soil, plants, and animals. It's crucial for protecting biodiversity and human health by assessing the risks of human activities like agriculture and industry on these environments.
This field studies contaminant sources, their movement through soil, and impacts on organisms. It involves toxicity testing, risk assessment, and developing strategies for cleaning up polluted sites. Understanding these processes helps create effective policies to safeguard terrestrial ecosystems.
Terrestrial toxicology overview
- Terrestrial toxicology focuses on the study of toxic substances and their effects on land-based ecosystems, including soil, plants, animals, and microorganisms
- Understanding the fate, transport, and impacts of contaminants in terrestrial environments is crucial for protecting biodiversity, ecosystem services, and human health
- Terrestrial toxicology plays a vital role in assessing and managing the risks associated with anthropogenic activities, such as agriculture, industry, and urbanization
Importance of terrestrial ecosystems
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- Terrestrial ecosystems provide essential services, such as nutrient cycling, carbon sequestration, water purification, and habitat for diverse species
- These ecosystems are critical for maintaining global biodiversity and supporting human well-being through the provision of food, fiber, and other resources
- Terrestrial environments are increasingly threatened by pollution, land-use changes, and climate change, highlighting the need for effective toxicological assessment and management
Major terrestrial habitats
- Terrestrial habitats encompass a wide range of ecosystems, including forests, grasslands, deserts, tundra, and wetlands
- Each habitat has unique characteristics, such as soil type, vegetation structure, and climatic conditions, which influence the fate and effects of contaminants
- Examples of major terrestrial habitats include tropical rainforests (Amazon), temperate grasslands (North American prairies), and boreal forests (taiga)
Soil contamination
- occurs when pollutants are introduced into the soil, either through direct application, accidental spills, or atmospheric deposition
- Contaminated soils can have adverse effects on plant growth, animal health, and ecosystem functioning, as well as pose risks to human health through exposure pathways such as ingestion, inhalation, and dermal contact
- Common soil contaminants include (lead, cadmium), (PCBs, DDT), and petroleum hydrocarbons
Sources of soil pollution
- Soil pollution can originate from various sources, including agricultural practices (, fertilizers), industrial activities (mining, manufacturing), and urban development (waste disposal, transportation)
- Atmospheric deposition of pollutants, such as acid rain and particulate matter, can also contribute to soil contamination
- Accidental spills and leaks from storage facilities or during transportation of hazardous materials are another significant source of soil pollution
Fate and transport of contaminants in soil
- The fate and transport of contaminants in soil depend on various physical, chemical, and biological processes, such as adsorption, desorption, degradation, and leaching
- Soil properties, including texture, organic matter content, pH, and cation exchange capacity, influence the mobility and persistence of contaminants
- Contaminants can be transported through soil via diffusion, advection, and dispersion processes, potentially leading to groundwater contamination or uptake by plants and animals
Bioavailability of soil contaminants
- Bioavailability refers to the fraction of a contaminant that is available for uptake by organisms or interaction with biological receptors
- Factors affecting bioavailability include contaminant speciation, soil properties, and the physiology of the exposed organisms
- Bioavailability is a critical factor in determining the toxicity and risk associated with soil contaminants, as it influences the exposure and potential adverse effects on terrestrial biota
Effects of soil properties on toxicity
- Soil properties can significantly influence the toxicity of contaminants by modifying their bioavailability, mobility, and persistence
- Soil pH affects the speciation and solubility of metal contaminants, with acidic conditions generally increasing their bioavailability and toxicity
- Organic matter content can bind and immobilize contaminants, reducing their bioavailability and potential toxicity
- Soil texture and structure influence the retention and transport of contaminants, with fine-textured soils (clays) generally having higher adsorption capacity than coarse-textured soils (sands)
Uptake and bioaccumulation in terrestrial organisms
- Uptake and of contaminants in terrestrial organisms are important processes that can lead to adverse effects and transfer of pollutants through food chains
- Plants and animals can accumulate contaminants from soil, water, and air, potentially reaching toxic levels that impact their health and survival
- Bioaccumulation occurs when the rate of contaminant uptake exceeds the rate of elimination, resulting in increasing concentrations over time
Plant uptake mechanisms
- Plants can take up contaminants from soil through their roots via passive diffusion or active transport processes
- The uptake of contaminants depends on factors such as plant species, root morphology, and the physicochemical properties of the contaminants
- Once absorbed, contaminants can be translocated to different plant parts (stems, leaves, fruits) and potentially enter the food chain through herbivory
Accumulation in terrestrial food chains
- Contaminants can accumulate in terrestrial food chains through dietary transfer, as organisms consume contaminated plants or prey
- of contaminants can lead to higher concentrations in organisms at higher trophic levels, a process known as
- Examples of contaminants that can accumulate in terrestrial food chains include mercury, PCBs, and DDT
Biomagnification of persistent pollutants
- Biomagnification is the process by which contaminant concentrations increase at successive trophic levels in a food chain
- Persistent pollutants, such as PCBs and DDT, are particularly susceptible to biomagnification due to their lipophilic nature and resistance to degradation
- Biomagnification can result in high contaminant loads in top predators (birds of prey, mammals), posing significant risks to their health and reproduction
Toxicity testing in terrestrial systems
- Toxicity testing in terrestrial systems involves assessing the adverse effects of contaminants on soil organisms, plants, and animals
- Various standardized test methods and protocols have been developed to evaluate the toxicity of chemicals and environmental samples in terrestrial ecosystems
- Toxicity tests provide valuable information for risk assessment, regulatory decision-making, and the development of soil quality guidelines
Soil toxicity tests
- assess the effects of contaminants on soil organisms, such as earthworms, springtails, and nematodes
- Common endpoints in soil toxicity tests include survival, reproduction, and growth of the test organisms
- Examples of standardized soil toxicity tests include the earthworm acute toxicity test (OECD 207) and the collembolan reproduction test (ISO 11267)
Plant toxicity tests
- Plant toxicity tests evaluate the impact of contaminants on seed germination, seedling emergence, and plant growth
- These tests can be conducted in soil or hydroponic systems, using a variety of plant species (monocots, dicots)
- Standardized plant toxicity tests include the seedling emergence and seedling growth test (OECD 208) and the vegetative vigor test (OCSPP 850.4150)
Invertebrate and vertebrate toxicity tests
- Invertebrate and vertebrate toxicity tests assess the effects of contaminants on higher trophic level organisms in terrestrial ecosystems
- Invertebrate tests may include the use of insects (honeybees, beetles) or other arthropods to evaluate acute or chronic toxicity
- Vertebrate tests often involve the use of birds (quail, mallard) or mammals (mice, rats) to assess toxicity through dietary or dermal exposure
Microbial toxicity tests
- Microbial toxicity tests evaluate the impact of contaminants on soil microbial communities and their functions
- These tests can assess endpoints such as microbial biomass, respiration, enzyme activities, and nitrogen transformation processes
- Examples of microbial toxicity tests include the soil microorganism: carbon transformation test (OECD 217) and the soil microorganism: nitrogen transformation test (OECD 216)
Terrestrial risk assessment
- Terrestrial risk assessment is the process of evaluating the likelihood and severity of adverse effects on terrestrial ecosystems and organisms resulting from exposure to contaminants
- Risk assessment involves four main steps: , , dose-response assessment, and risk characterization
- The goal of terrestrial risk assessment is to provide a scientific basis for decision-making and the development of risk management strategies
Exposure assessment in terrestrial environments
- Exposure assessment in terrestrial environments involves estimating the concentrations and duration of contaminant exposure for different ecological receptors
- This step considers the sources, pathways, and routes of exposure, as well as the spatial and temporal distribution of contaminants
- Exposure assessment may involve field sampling, monitoring data, or modeling approaches to quantify contaminant levels in soil, plants, and animals
Hazard identification and dose-response assessment
- Hazard identification involves determining the potential adverse effects associated with a contaminant based on its toxicological properties and mode of action
- Dose-response assessment establishes the relationship between the dose or exposure level of a contaminant and the magnitude of the observed adverse effects
- This step often relies on toxicity test data and extrapolation methods to derive benchmark values (e.g., ECx, NOEC) for risk characterization
Risk characterization for terrestrial ecosystems
- Risk characterization integrates the information from exposure and dose-response assessments to estimate the likelihood and severity of adverse effects on terrestrial ecosystems
- This step may involve the calculation of risk quotients (RQs) by comparing exposure levels to toxicity benchmarks or the use of probabilistic methods to quantify uncertainty
- Risk characterization provides a basis for determining the acceptability of risks and informing risk management decisions
Ecological risk assessment frameworks
- Ecological risk assessment frameworks provide structured approaches for evaluating and managing risks to terrestrial ecosystems
- These frameworks typically follow a tiered approach, starting with conservative screening-level assessments and progressing to more refined and site-specific evaluations as needed
- Examples of ecological risk assessment frameworks include the US EPA's Ecological Risk Assessment Guidance for Superfund (ERAGS) and the European Food Safety Authority's (EFSA) Guidance on Ecological Risk Assessment
Remediation of contaminated terrestrial sites
- Remediation of contaminated terrestrial sites involves the application of technologies and strategies to reduce or eliminate the risks posed by soil contaminants
- The selection of remediation approaches depends on factors such as the type and extent of contamination, site characteristics, and remediation goals
- Remediation technologies can be broadly categorized into in situ (on-site) and ex situ (off-site) methods
In situ vs ex situ remediation techniques
- In situ remediation techniques treat contaminated soil in place, without excavation or removal
- Examples of in situ remediation techniques include , , and soil vapor extraction
- Ex situ remediation involves the excavation and treatment of contaminated soil off-site, using methods such as thermal desorption, soil washing, or landfilling
- In situ techniques are often preferred due to lower costs and reduced environmental disturbance, while ex situ methods may be necessary for highly contaminated or complex sites
Bioremediation strategies
- Bioremediation involves the use of microorganisms to degrade or transform contaminants into less toxic or non-toxic forms
- Bioremediation strategies can be classified as intrinsic (natural attenuation) or engineered (biostimulation, bioaugmentation)
- Intrinsic bioremediation relies on the natural degradation capacity of indigenous microorganisms, while engineered approaches involve the addition of nutrients, oxygen, or specific microbial strains to enhance degradation rates
- Bioremediation is particularly effective for organic contaminants, such as petroleum hydrocarbons and certain pesticides
Phytoremediation and plant-based approaches
- Phytoremediation is the use of plants to remove, degrade, or stabilize contaminants in soil
- Plants can contribute to remediation through various mechanisms, including phytoextraction (uptake and accumulation), phytodegradation (enzymatic transformation), and phytostabilization (immobilization in the root zone)
- Phytoremediation is a cost-effective and environmentally friendly approach, particularly for large-scale, low-concentration contamination
- Examples of plants used in phytoremediation include hyperaccumulators (Thlaspi caerulescens for cadmium) and fast-growing trees (Populus spp. for organic contaminants)
Soil washing and chemical treatments
- Soil washing involves the physical separation of contaminated soil particles from the clean soil matrix using water or chemical solutions
- This process concentrates the contaminants into a smaller volume of soil, which can then be further treated or disposed of
- Chemical treatments, such as oxidation or reduction, can be used to degrade or immobilize contaminants in soil
- Examples of chemical treatments include the use of hydrogen peroxide (Fenton's reagent) for the oxidation of organic contaminants and the application of phosphate amendments for the immobilization of heavy metals
Regulatory aspects of terrestrial toxicology
- Regulatory aspects of terrestrial toxicology involve the development and implementation of laws, guidelines, and policies to protect terrestrial ecosystems from the adverse effects of contaminants
- Regulatory frameworks aim to set acceptable limits for contaminant levels in soil, establish monitoring and assessment requirements, and guide the management and remediation of contaminated sites
- Effective regulation requires the integration of scientific knowledge, risk assessment, and stakeholder engagement
Soil quality guidelines and standards
- Soil quality guidelines and standards provide benchmark values for assessing the acceptability of contaminant levels in soil
- These values are typically derived based on toxicological data, risk assessment, and consideration of land use scenarios (residential, agricultural, industrial)
- Examples of soil quality guidelines include the US EPA's Regional Screening Levels (RSLs) and the Canadian Council of Ministers of the Environment's (CCME) Soil Quality Guidelines
Environmental monitoring and assessment
- Environmental monitoring and assessment involve the systematic collection and analysis of data to evaluate the status and trends of contaminants in terrestrial ecosystems
- Monitoring programs may include soil sampling, biological surveys, and the measurement of contaminant levels in plants and animals
- Assessment approaches, such as the Triad approach, integrate chemical, toxicological, and ecological data to provide a comprehensive evaluation of site conditions and risks
Ecological restoration and habitat management
- Ecological restoration and habitat management are important components of regulatory frameworks for terrestrial ecosystems
- Restoration aims to assist the recovery of degraded or contaminated habitats, promoting the return of native species and ecological functions
- Habitat management involves the active intervention and maintenance of terrestrial ecosystems to support biodiversity and ecosystem services
- Regulatory requirements may include the development of restoration plans, monitoring of restoration success, and the implementation of best management practices
Policy and decision-making for terrestrial protection
- Policy and decision-making for terrestrial protection involve the development and implementation of strategies to prevent, mitigate, and manage the impacts of contaminants on terrestrial ecosystems
- This process requires the integration of scientific evidence, risk assessment, economic considerations, and stakeholder perspectives
- Effective policy and decision-making rely on transparent and participatory processes, as well as the use of adaptive management approaches to address uncertainties and changing conditions
- Examples of relevant policies include the US Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and the European Union's Soil Thematic Strategy
Key Terms to Review (21)
Bioaccumulation: Bioaccumulation is the process by which organisms accumulate toxic substances from their environment, leading to higher concentrations of these substances within their tissues over time. This phenomenon is crucial for understanding how pollutants, like heavy metals or pesticides, can persist and magnify through food webs, impacting both ecosystems and human health.
Bioassays: Bioassays are experimental procedures used to assess the effects of a substance on living organisms, often utilized to measure the potency and toxicity of chemicals. They provide crucial data on how various substances interact with biological systems, allowing scientists to evaluate the impact of environmental contaminants or pharmaceuticals. Bioassays can be designed for different organisms, including plants and animals, making them versatile tools in understanding terrestrial toxicology and decontamination methods.
Biomagnification: Biomagnification is the process where the concentration of toxic substances increases in organisms at each successive level of the food chain. This phenomenon highlights how contaminants, such as pesticides and heavy metals, can accumulate in the bodies of organisms and become more concentrated as they move up trophic levels, impacting not only individual species but entire ecosystems.
Bioremediation: Bioremediation is the process of using living organisms, typically microorganisms, to remove or neutralize contaminants from soil and water. This technique leverages the natural metabolic processes of these organisms to degrade harmful substances, making it an effective strategy for cleaning up polluted environments. By connecting bioremediation to concepts like bioaccumulation and biomagnification, we can see its potential to mitigate the harmful effects of toxic substances that accumulate in ecosystems over time.
Ecotoxicology: Ecotoxicology is the study of the effects of toxic substances on the environment, particularly on ecosystems and the organisms that inhabit them. It examines how pollutants impact various levels of biological organization, from individual organisms to populations and communities. This field is critical for understanding the risks associated with chemicals in the environment and plays a key role in assessing the health of terrestrial ecosystems and evaluating the safety of substances through in vivo testing methods.
Endocrine Disruption: Endocrine disruption refers to the interference of chemicals with the endocrine system, which regulates hormones that control various biological processes. These disruptions can lead to a range of health issues, including reproductive problems, developmental delays, and metabolic disorders. Understanding endocrine disruption is crucial as it connects to toxicological endpoints, the impact of pesticides, and terrestrial toxicology.
Exposure Assessment: Exposure assessment is the process of estimating or measuring the magnitude, frequency, and duration of human or ecological exposure to an agent, such as chemicals or biological contaminants. This concept is crucial in understanding how different agents, like pesticides or pollutants, can affect health and the environment, while also forming the foundation for risk assessment, regulatory guidelines, and public health decisions.
Hazard Identification: Hazard identification is the process of recognizing and assessing potential sources of harm or adverse effects in various environments, particularly concerning toxic substances. This process is crucial for understanding the risks associated with exposure to chemicals, guiding toxicity testing methods, evaluating ecological impacts, assessing human exposure, characterizing risks, and ensuring compliance with regulatory guidelines.
Heavy metals: Heavy metals are metallic elements with high atomic weights and densities, typically greater than 5 g/cm³, that can be toxic at low concentrations. They are significant in various fields of study due to their potential harmful effects on human health and the environment, linking them to various toxicological endpoints and types of toxicity.
Neurotoxicity: Neurotoxicity refers to the damage or dysfunction of nerve cells caused by exposure to toxic substances, which can lead to various neurological disorders and impairments. This phenomenon can occur due to a wide range of chemicals, including pesticides, heavy metals, solvents, and natural toxins, impacting the nervous system's function and health.
Persistent Organic Pollutants: Persistent organic pollutants (POPs) are toxic chemical compounds that resist environmental degradation and remain in the environment for long periods. These pollutants can bioaccumulate in the food chain and pose serious risks to human health and ecosystems, making them a critical concern in terrestrial environments. Their longevity and ability to travel long distances through air and water make them a widespread issue that requires attention from policymakers and environmental scientists.
Pesticides: Pesticides are chemical substances used to prevent, destroy, or control pests, including insects, weeds, fungi, and rodents. They play a critical role in agriculture and public health but can also pose risks to non-target organisms, leading to various toxicological endpoints that can affect ecosystems and human health.
Phytoremediation: Phytoremediation is an environmental cleanup technology that uses plants to remove, transfer, stabilize, or destroy contaminants in soil and water. This method leverages the natural abilities of certain plants to absorb pollutants, making it a cost-effective and sustainable approach to remediation. By utilizing plant systems, phytoremediation not only helps in reducing toxic substances but also aids in restoring ecological balance.
Phytotoxicity: Phytotoxicity refers to the toxic effects that certain substances can have on plants, inhibiting their growth, development, or physiological functions. This phenomenon is essential in understanding how chemicals, whether natural or synthetic, impact terrestrial ecosystems and agricultural productivity. It encompasses various interactions between plants and pollutants, including herbicides, heavy metals, and other environmental stressors that can lead to adverse effects on plant health.
Rachel Carson: Rachel Carson was an influential American marine biologist, author, and conservationist whose work raised awareness about environmental issues and the dangers of pesticide use, particularly DDT. Her book 'Silent Spring' challenged the practices of agricultural scientists and the government, sparking a nationwide environmental movement that continues to influence toxicology and environmental policy today.
Reach: In toxicology, 'reach' refers to the extent or range of exposure to a toxic substance that can affect organisms and ecosystems. Understanding the reach of a toxic agent is crucial for evaluating its potential impacts on human health and the environment, as it encompasses factors such as concentration, duration, and routes of exposure.
Soil contamination: Soil contamination refers to the presence of hazardous substances in the soil, resulting from human activities, industrial processes, agricultural practices, or waste disposal. This pollution can affect soil quality and health, leading to adverse effects on plants, animals, and humans. Understanding soil contamination is crucial for assessing risks related to metals and its impact on terrestrial ecosystems.
Soil toxicity tests: Soil toxicity tests are assessments used to evaluate the harmful effects of contaminants on soil organisms and the overall health of soil ecosystems. These tests help determine how toxic substances, like heavy metals, pesticides, or industrial chemicals, affect the biological activity and diversity in the soil. By understanding soil toxicity, we can better manage land use and protect both environmental quality and human health.
Toxic Substances Control Act: The Toxic Substances Control Act (TSCA) is a United States law enacted in 1976 that gives the Environmental Protection Agency (EPA) the authority to regulate the introduction of new or existing chemicals. This law plays a critical role in ensuring that chemicals used in commerce do not pose unreasonable risks to human health or the environment, thereby influencing various aspects of toxicology, including history, factors affecting toxicity, and specific toxicological concerns such as endocrine disruption and neurotoxicity.
Trophic transfer: Trophic transfer refers to the movement of substances, including toxicants, through food webs as one organism consumes another. This process highlights how contaminants can accumulate and magnify in organisms at higher trophic levels, creating significant ecological and health implications. Understanding trophic transfer is crucial for assessing the fate and effects of toxicants in ecosystems, particularly regarding bioaccumulation and biomagnification.
U.S. Environmental Protection Agency: The U.S. Environmental Protection Agency (EPA) is a federal agency established in 1970 to protect human health and the environment by enforcing regulations based on laws passed by Congress. The EPA plays a crucial role in monitoring and regulating pollutants and hazardous substances, contributing significantly to the field of terrestrial toxicology by assessing the impact of chemicals on soil, water, and living organisms.