🐠Ecotoxicology Unit 11 – Emerging Contaminants: Micro to Nano Scale

Key Concepts and Definitions

• Emerging contaminants are substances recently discovered or characterized in the environment not commonly monitored but have potential adverse effects
• Include pharmaceuticals, personal care products, endocrine disruptors, nanoparticles, microplastics, and more
• Contaminants of emerging concern (CECs) pose unique challenges due to limited data on occurrence, fate, and toxicity
• Micropollutants are contaminants present in trace concentrations (parts per billion or trillion) but can still have significant impacts on ecosystems
• Persistence refers to a contaminant's ability to remain in the environment without degrading or transforming
  • Persistent organic pollutants (POPs) are a class of highly persistent contaminants that bioaccumulate and have long-range transport potential
• Bioaccumulation occurs when a substance is absorbed by an organism faster than it can be metabolized or excreted, leading to higher concentrations in tissues over time
• Biomagnification is the increasing concentration of a substance in tissues as it moves up the food chain due to bioaccumulation at each trophic level

Sources and Types of Emerging Contaminants

• Wastewater treatment plants are a major source of emerging contaminants, as many are not effectively removed by conventional treatment processes
• Agricultural runoff can contain emerging contaminants such as veterinary pharmaceuticals, hormones, and pesticides
• Industrial discharges may include a wide range of emerging contaminants depending on the specific processes and materials used
• Pharmaceuticals and personal care products (PPCPs) enter the environment through human use and improper disposal
  • Examples include antibiotics, hormones, antidepressants, and UV filters from sunscreens
• Endocrine-disrupting chemicals (EDCs) interfere with the normal functioning of hormones in organisms and can come from various sources (plasticizers, pesticides, and industrial compounds)
• Nanoparticles, which have at least one dimension less than 100 nanometers, are increasingly used in consumer products and industrial applications, leading to their release into the environment
• Microplastics, plastic particles less than 5 millimeters in size, originate from the breakdown of larger plastic debris or are intentionally added to products (microbeads in cosmetics)

Environmental Fate and Transport

• The fate and transport of emerging contaminants depend on their physicochemical properties and environmental conditions
• Sorption to soil and sediment can immobilize contaminants, but they may still be bioavailable to organisms or transported via erosion
• Volatilization allows some contaminants to enter the atmosphere and undergo long-range transport before deposition
• Photodegradation by sunlight can break down some contaminants, but the process is often incomplete and may produce toxic byproducts
• Biodegradation by microorganisms is a key removal mechanism for many organic contaminants, but some are resistant to microbial degradation
• Hydrolysis, the reaction of a substance with water, can lead to the transformation of some contaminants
• Transport in surface water and groundwater can spread emerging contaminants far from their original sources
  • Factors such as water solubility, adsorption to particles, and environmental persistence influence the extent of transport

Detection and Analytical Methods

• Detecting and quantifying emerging contaminants requires advanced analytical techniques due to their low concentrations and diverse chemical structures
• Liquid chromatography-mass spectrometry (LC-MS) is widely used for the analysis of polar and non-volatile contaminants, offering high sensitivity and selectivity
  • Tandem mass spectrometry (LC-MS/MS) provides even greater specificity by using multiple stages of mass analysis
• Gas chromatography-mass spectrometry (GC-MS) is suitable for volatile and semi-volatile contaminants, often requiring derivatization to improve detection
• High-resolution mass spectrometry (HRMS) techniques, such as time-of-flight (TOF) and Orbitrap, enable the identification of unknown contaminants based on accurate mass measurements
• Immunoassays, such as enzyme-linked immunosorbent assay (ELISA), use antibodies to detect specific contaminants and can be used for rapid screening
• Biosensors employ biological elements (enzymes, antibodies, or cells) to generate a measurable signal in the presence of a target contaminant
• Sample preparation techniques, including solid-phase extraction (SPE) and liquid-liquid extraction (LLE), are crucial for isolating and concentrating emerging contaminants from complex environmental matrices
• Quality assurance and quality control (QA/QC) procedures, such as using certified reference materials and assessing method performance, ensure the reliability of analytical results

Ecotoxicological Effects

• Emerging contaminants can have diverse toxic effects on organisms, depending on the specific contaminant, concentration, and species exposed
• Endocrine disruption is a major concern, as EDCs can interfere with hormone signaling and lead to reproductive, developmental, and metabolic disorders
  • Examples include feminization of male fish exposed to estrogenic compounds and impaired shell development in mollusks exposed to tributyltin
• Antibiotic resistance can develop in bacteria exposed to sub-therapeutic levels of antibiotics in the environment, potentially compromising the effectiveness of these drugs in treating infections
• Nanoparticles may exhibit unique toxicological properties due to their small size and high surface area-to-volume ratio, potentially causing oxidative stress or cellular damage
• Microplastics can be ingested by organisms and cause physical damage, false satiation, or act as vectors for other contaminants
• Mixture toxicity is a challenge in assessing the effects of emerging contaminants, as organisms are often exposed to multiple contaminants simultaneously, which can lead to additive, synergistic, or antagonistic interactions
• Sublethal effects, such as changes in behavior, growth, or reproduction, may occur at lower concentrations than those causing acute toxicity and can have population-level impacts over time
• Ecological risk assessment aims to characterize the likelihood and magnitude of adverse effects on ecosystems based on exposure and toxicity data for emerging contaminants

Risk Assessment and Management

• Risk assessment for emerging contaminants involves four main steps: hazard identification, dose-response assessment, exposure assessment, and risk characterization
• Hazard identification involves determining the potential adverse effects of a contaminant based on toxicological studies and mode of action
• Dose-response assessment establishes the relationship between the dose of a contaminant and the likelihood or severity of an adverse effect
  • This step often involves extrapolating from high-dose animal studies to low-dose human or ecological exposures
• Exposure assessment estimates the magnitude, frequency, and duration of exposure to a contaminant based on environmental monitoring data and fate and transport modeling
• Risk characterization integrates information from the previous steps to estimate the probability and magnitude of adverse effects under specific exposure scenarios
• Uncertainty analysis is a critical component of risk assessment, as it helps to identify data gaps and limitations in the available information
• Risk management involves deciding on actions to mitigate or prevent unacceptable risks, considering factors such as technical feasibility, cost-effectiveness, and societal values
  • Examples include source control, treatment technologies, and regulatory measures (e.g., setting environmental quality standards or product bans)

Regulatory Frameworks and Challenges

• Regulatory frameworks for emerging contaminants vary widely across jurisdictions and often lag behind scientific understanding of their risks
• The precautionary principle, which states that lack of full scientific certainty should not preclude preventive action in the face of potentially serious or irreversible harm, is sometimes applied to emerging contaminants
• The European Union's REACH (Registration, Evaluation, Authorization, and Restriction of Chemicals) regulation requires manufacturers and importers to assess and manage the risks of chemicals, including emerging contaminants
• In the United States, the Toxic Substances Control Act (TSCA) and the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) are the primary laws governing the regulation of chemicals, but they have limitations in addressing emerging contaminants
• The Stockholm Convention on Persistent Organic Pollutants is an international treaty that aims to eliminate or restrict the production and use of POPs, some of which are considered emerging contaminants
• Challenges in regulating emerging contaminants include the large number of substances, limited toxicity and exposure data, and the need to balance risks and benefits (e.g., for pharmaceuticals)
• Prioritization frameworks, such as the US EPA's Contaminant Candidate List (CCL) for drinking water, help to focus research and regulatory efforts on the most pressing emerging contaminants
• Stakeholder engagement, including industry, academia, government agencies, and the public, is essential for developing effective and socially acceptable strategies for managing emerging contaminants

Future Research and Innovations

• Advances in analytical chemistry, such as non-targeted screening and high-resolution mass spectrometry, will continue to improve our ability to detect and identify emerging contaminants
• Environmental monitoring programs should be expanded to include a wider range of emerging contaminants and to better characterize their occurrence and fate in different environmental compartments
• Toxicity testing approaches, such as high-throughput screening and omics technologies (genomics, proteomics, and metabolomics), can help to elucidate the mechanisms of action and potential adverse effects of emerging contaminants
• Ecological risk assessment methods should be refined to better account for the complexity of environmental exposures, including mixture effects and multiple stressors
• Green and sustainable chemistry principles should be applied in the design and production of chemicals to minimize their environmental impact and prevent the emergence of new contaminants
  • This includes the development of safer alternatives to problematic substances and the use of more efficient and environmentally friendly manufacturing processes
• Advanced treatment technologies, such as advanced oxidation processes and membrane filtration, should be further developed and optimized for the removal of emerging contaminants from water and wastewater
• Nature-based solutions, such as constructed wetlands and bioremediation, can offer cost-effective and environmentally friendly approaches for managing emerging contaminants
• Collaborative research efforts, involving interdisciplinary teams and international cooperation, are essential for addressing the global challenge of emerging contaminants and developing innovative solutions