Ecotoxicology

🐠Ecotoxicology Unit 6 – Acute and Chronic Toxicity in Individuals

Acute and chronic toxicity in individuals are crucial concepts in ecotoxicology. They describe how substances harm organisms over different time scales. Understanding these effects helps scientists assess environmental risks and develop protective measures for ecosystems. Toxicity testing methods, dose-response relationships, and biomarkers are key tools for studying toxicity. Environmental factors like temperature and pH can influence toxicity. Real-world applications include risk assessment, ecological restoration, and bioremediation to address toxicant impacts on ecosystems.

Key Concepts and Definitions

  • Toxicity refers to the degree to which a substance can harm an organism
  • Acute toxicity occurs rapidly after exposure to a single dose or multiple doses over a short period (usually less than 24 hours)
  • Chronic toxicity develops slowly and occurs after repeated or long-term exposure to a substance
  • Dose-response relationship describes how the likelihood and severity of adverse health effects change as the amount of exposure to a stressor increases
  • Toxicants are substances that can injure or kill living organisms through chemical activity
  • Biomarkers are measurable indicators of a biological state or condition used to assess exposure, effect, or susceptibility
  • Toxicodynamics studies the biochemical and physiological effects of toxicants on living organisms
  • Toxicokinetics examines the absorption, distribution, metabolism, and excretion of toxicants in living organisms

Types of Toxicity

  • Acute toxicity is characterized by rapid onset and short duration of effects after exposure to a single dose or multiple doses over a short period
  • Chronic toxicity develops slowly over an extended period due to repeated or continuous exposure to a substance
  • Subchronic toxicity occurs from repeated exposure for more than one month but less than the lifetime of the organism
  • Developmental toxicity affects the developing offspring during any stage of development before birth
  • Reproductive toxicity impacts sexual function, fertility, and offspring of exposed individuals
  • Carcinogenicity is the ability of a substance to cause cancer or increase its incidence
  • Neurotoxicity affects the structure or function of the central and/or peripheral nervous system
  • Immunotoxicity alters the structure or function of the immune system, increasing the risk of adverse health outcomes

Mechanisms of Toxicity

  • Toxicants can disrupt cellular processes by binding to receptors, altering gene expression, or interfering with signaling pathways
  • Oxidative stress occurs when the generation of reactive oxygen species exceeds the body's ability to neutralize them, leading to cellular damage
  • DNA damage and mutations can result from exposure to genotoxic substances, potentially causing cancer or birth defects
  • Enzyme inhibition can disrupt essential metabolic processes (cytochrome P450 enzymes)
  • Membrane damage can lead to cell lysis and tissue injury
  • Endocrine disruption occurs when toxicants interfere with the synthesis, secretion, transport, binding, action, or elimination of natural hormones
  • Mitochondrial dysfunction can impair energy production and lead to cell death
  • Epigenetic changes, such as DNA methylation and histone modifications, can alter gene expression without changing the DNA sequence

Dose-Response Relationships

  • Dose-response relationships describe how the likelihood and severity of adverse health effects change as the amount of exposure to a stressor increases
  • Threshold dose is the minimum dose required to produce a detectable effect
  • No Observed Adverse Effect Level (NOAEL) is the highest dose at which no statistically or biologically significant adverse effects are observed
  • Lowest Observed Adverse Effect Level (LOAEL) is the lowest dose at which statistically or biologically significant adverse effects are observed
  • Benchmark dose (BMD) is the dose that produces a predetermined change in response rate of an adverse effect compared to background
  • Hormesis is a biphasic dose-response phenomenon characterized by low-dose stimulation and high-dose inhibition
  • Linear dose-response relationships exhibit a directly proportional relationship between dose and effect
  • Non-linear dose-response relationships display a complex relationship between dose and effect (threshold, sigmoidal, or U-shaped curves)

Toxicity Testing Methods

  • In vitro tests are conducted using isolated cells, tissues, or organs to assess the toxicity of a substance
    • Cell viability assays (MTT, LDH) measure the proportion of living cells after exposure to a toxicant
    • Genotoxicity tests (Ames test, comet assay) evaluate the ability of a substance to cause DNA damage
  • In vivo tests involve whole living organisms to evaluate the toxicity of a substance
    • Acute toxicity tests (LD50, LC50) determine the dose that causes mortality in 50% of the test organisms
    • Subchronic and chronic toxicity tests assess the effects of repeated exposure over a portion of the lifespan or the entire lifespan of the test organism
  • In silico methods use computer models and simulations to predict the toxicity of a substance based on its structure and properties
  • High-throughput screening (HTS) employs automated equipment to rapidly test large numbers of compounds for potential toxicity
  • Omics technologies (genomics, proteomics, metabolomics) provide a comprehensive analysis of the biological response to toxicant exposure

Biomarkers and Indicators

  • Biomarkers are measurable indicators of a biological state or condition used to assess exposure, effect, or susceptibility
  • Exposure biomarkers indicate the presence of a toxicant in an organism (blood lead levels)
  • Effect biomarkers reflect the biological response to toxicant exposure (enzyme activity, DNA adducts)
  • Susceptibility biomarkers identify individuals with increased sensitivity to toxicant exposure (genetic polymorphisms)
  • Bioindicators are organisms or communities used to assess the quality of the environment and how it changes over time
    • Sentinel species are sensitive to specific environmental stressors and serve as early warning signs of ecosystem health (amphibians, bivalves)
  • Biomonitoring involves the repeated measurement of biomarkers in a population to assess exposure and health status over time
  • Bioaccumulation occurs when a substance is absorbed by an organism at a rate faster than it is lost, leading to higher concentrations in the organism than in the environment

Environmental Factors Influencing Toxicity

  • Temperature can affect the uptake, metabolism, and elimination of toxicants in organisms
    • Higher temperatures generally increase the rate of uptake and metabolism, potentially enhancing toxicity
  • pH influences the speciation, solubility, and bioavailability of toxicants in the environment
    • Acidic conditions can increase the mobility and toxicity of metals (aluminum in acidified lakes)
  • Salinity can impact the osmotic balance and ion regulation in aquatic organisms, modifying their sensitivity to toxicants
  • Dissolved oxygen levels affect the respiratory capacity and energy metabolism of aquatic organisms, influencing their response to toxicants
  • Nutrient availability can modulate the growth, reproduction, and detoxification capabilities of organisms
  • Light intensity and photoperiod can influence the production of reactive oxygen species and the toxicity of phototoxic compounds
  • Habitat quality and complexity can provide refuge and resources for organisms, mitigating the effects of toxicant exposure

Real-World Applications and Case Studies

  • Environmental risk assessment evaluates the likelihood and consequences of adverse effects from toxicant exposure in ecosystems
    • Hazard identification determines the potential of a substance to cause harm
    • Exposure assessment estimates the magnitude, frequency, and duration of exposure
    • Dose-response assessment quantifies the relationship between dose and effect
    • Risk characterization integrates information from the previous steps to estimate the probability and severity of adverse effects
  • Ecological restoration aims to restore degraded ecosystems and mitigate the impacts of toxicant contamination (Deepwater Horizon oil spill)
  • Bioremediation uses microorganisms to break down and detoxify pollutants in the environment (petroleum hydrocarbons, chlorinated solvents)
  • Phytoremediation employs plants to absorb, accumulate, and detoxify contaminants from soil and water (heavy metals, organic pollutants)
  • Ecotoxicological modeling predicts the fate, transport, and effects of toxicants in the environment using mathematical and computational tools
  • Regulatory agencies (EPA, ECHA) use ecotoxicological data to establish environmental quality standards and regulate the use and disposal of chemicals
  • Ecotoxicological research advances our understanding of the mechanisms and consequences of toxicant exposure in ecosystems, informing conservation and management strategies


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ÂĐ 2024 Fiveable Inc. All rights reserved.
APÂŪ and SATÂŪ are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.