Release of Chemicals into the Environment

Pathways of Chemical Release into the Environment

Chemicals can enter the environment at every stage of their “life cycle”: raw material extraction, production, use, recycling, and disposal. The key aspect in this chapter is how substances leave controlled technical systems and become part of air, water, soil, and living organisms.

Life Cycle Perspective

For any chemical or product (e.g. a plasticizer, a pesticide, a detergent), one can distinguish typical stages where emissions occur:

• Production and processing
• Losses during synthesis (unreacted starting materials, by-products).
• Fugitive emissions from valves, pumps, storage tanks.
• Accidental releases (leaks, spills, explosions).
• Formulation and packaging
• Dust and vapors when mixing powders and liquids.
• Residues in containers that are not properly cleaned.
• Use (application phase)
• Intentional releases (pesticides, fertilizers, road salt).
• Evaporation of volatile components (solvents in paints, fuels).
• Abrasion and wear (tire particles, brake dust, microplastics from textiles).
• Leaching from materials (plasticizers from PVC, flame retardants from electronics).
• End-of-life
• Emissions from waste storage and landfills (leachate, landfill gas).
• Incomplete destruction during incineration (formation of persistent by-products).
• Uncontrolled dumping, open burning, and littering.

This “cradle-to-grave” view is essential to understand where intervention is most effective.

Types of Sources: Point, Line, and Diffuse

Chemicals are not released in the same way everywhere. For environmental assessment and regulation, it is important to distinguish source types.

Point Sources

A point source is a geographically localized, usually identifiable emission point.

Typical examples:

• A factory’s wastewater outlet into a river.
• A chimney stack of a power plant or waste incinerator.
• A chemical storage tank with a leaking valve.

Characteristics:

• Emissions can often be measured and monitored directly at the outlet.
• Technical measures (filters, scrubbers, wastewater treatment) can be installed at the source.
• Regulations can impose discharge limits and require permits.

Point sources are often the first targets of environmental protection measures because they are relatively easy to control.

Line Sources

Line sources are extended, linear emission sources.

Examples:

• Busy roads and highways (exhaust gases, tire and brake particles).
• Railway lines (abrasion of rails and wheels, brake wear).
• Pipelines with small leaks along their length.

Characteristics:

• Emissions affect a corridor along the line.
• Monitoring is more complex than for single points.
• Control measures include cleaner fuels, emission standards for vehicles, and noise/dust barriers.

Diffuse (Area) Sources

Diffuse sources are spatially widespread and often not directly linked to a single facility or user.

Examples:

• Application of pesticides and fertilizers over agricultural land.
• Household use of detergents, cosmetics, and cleaning agents.
• Evaporation of solvents from many small workshops.
• Deposition of air pollutants over large regions.

Characteristics:

• Emissions are the sum of many small individual contributions.
• Often poorly quantifiable; estimates rely on models and usage statistics.
• Control is largely through product regulation, labeling, and consumer behavior, not end-of-pipe treatment.

Main Environmental Media and Transfer Processes

Once released, chemicals do not stay where they entered. They can move between environmental compartments: air, water, soil, sediments, and organisms.

Air as a Transport Path

Chemicals can enter the air:

• As gases or vapors (volatile organic compounds, some pesticides).
• Adsorbed to fine particles or dust (heavy metals, combustion by-products).
• As aerosols (tiny liquid or solid droplets).

Typical release pathways:

• Combustion processes (cars, power plants, domestic heating).
• Evaporation from solvents, fuels, and volatile consumer products.
• Industrial processes (metal smelting, chemical manufacturing).
• Open burning of waste.

Airborne chemicals can be transported over long distances and later deposited into water and soil by:

• Dry deposition: direct settling of particles and gases.
• Wet deposition: washout by rain or snow (“acid rain”, nutrient deposition).

Water as a Transport and Accumulation Path

Chemicals reach surface waters and groundwater via:

• Direct discharges (treated or untreated industrial and municipal wastewater).
• Runoff from fields and urban surfaces (pesticides, fertilizers, road salt, oil, microplastics).
• Leaching from contaminated soils, waste deposits, and landfills.
• Atmospheric deposition onto water surfaces.

In water, processes such as dissolution, adsorption to suspended solids, sedimentation, and uptake by organisms determine their further fate.

Soil and Sediments

Soil and sediment serve both as sinks and secondary sources:

• Deposition of airborne particles (e.g. heavy metals, soot).
• Infiltration of polluted water (e.g. pesticide-laden runoff, leaking sewer systems).
• Direct application of chemicals (fertilizers, pesticides, sewage sludge).

From soil and sediments, chemicals can:

• Be taken up by plants and soil organisms.
• Be mobilized again by erosion, leading to water contamination.
• Volatilize and return to the atmosphere.

Categories of Chemical Releases

Releases differ not only in where they occur but also in their intentionality and temporal pattern.

Intentional vs. Unintentional Releases

• Intentional releases
• The release is part of intended use.
• Examples: application of pesticides, spreading of fertilizers, addition of chlorine for disinfection in pools, use of road salt.
• Chemically, these uses can be considered “controlled emissions” that are accepted because of specific benefits.
• Unintentional releases
• Accidental spills (tank ruptures, transport accidents).
• Leakages from storage or pipelines.
• Formation of undesired by-products (e.g. dioxins during certain combustion conditions).
• Improper handling (overfilling, incorrect disposal, illegal dumping).

Prevention and emergency response plans are essential for limiting damage from unintentional releases.

Continuous vs. Episodic Emissions

• Continuous (or quasi-continuous) emissions
• Constant or regularly recurring emissions (chimney from a power plant, municipal wastewater treatment effluent, household discharges).
• Typically easier to monitor and regulate.
• Influence background contamination levels.
• Episodic emissions
• Short-term, sometimes high-intensity events.
• Examples: accidents, maintenance operations (tank cleaning), stormwater overflows, application of pesticides during a specific season.
• Environmental impacts can be severe locally and in the short term.

Examples of Important Release Pathways

To make these general principles concrete, consider a few common classes of chemicals and how they are typically released.

Pesticides

• Intended application to plants, soil, or seeds.
• Release paths:
• Direct spray to crops and nearby surfaces.
• Drift by wind to non-target areas.
• Wash-off by rain into surface waters.
• Infiltration into groundwater.
• Volatilization into the atmosphere (especially more volatile pesticides).

Control strategies focus on application techniques, timing, and product choice.

Nutrients (Fertilizers)

• Nitrogen and phosphorus compounds spread on fields.
• Release paths:
• Nitrate leaching into groundwater.
• Phosphate transport with eroded soil into surface waters.
• Emission of ammonia and nitrous oxide to the atmosphere.

These releases can lead to eutrophication of water bodies and contribute to climate-relevant gas emissions.

Industrial Organic Chemicals

Examples: solvents, plasticizers, surfactants, flame retardants.

• Release paths:
• Losses during production and formulation.
• Evaporation during use (solvents in paints and cleaning agents).
• Leaching from materials during use and disposal (e.g. plasticizers, flame retardants).
• Entry into wastewater through household and industrial use.

Persistent and bioaccumulative substances are of particular concern because they accumulate in ecosystems.

Metals and Metal Compounds

• Sources: mining, metal processing, combustion of coal and waste, traffic (brake linings, tires).
• Release paths:
• Dust and fumes into the air.
• Particles and dissolved ions in wastewater and runoff.
• Long-term release from contaminated soils and sediments.

Metals do not degrade; they can change chemical form but remain in the environment.

Microplastics and Nanomaterials

• Sources: fragmentation of larger plastic items, tire wear, synthetic fibers, personal care products, industrial uses.
• Release paths:
• Direct entry into wastewater (e.g. from washing machines, cosmetics).
• Runoff from roads.
• Degradation of litter in the environment.

Wastewater treatment plants can remove part of the microplastics, but some fraction passes through and enters surface waters.

Factors Influencing Environmental Release

Whether and how strongly a chemical is released depends on both substance properties and use patterns.

Substance Properties

Key physicochemical properties affecting release and distribution include:

• Volatility
• High vapor pressure → easier transition into the gas phase → stronger air emissions.
• Water solubility
• High solubility → easier dissolution into water and transport in aqueous systems.
• Partition behavior
• Tendency to bind to organic matter vs. remain in water or air.
• Persistence
• Resistance to chemical or biological degradation → longer residence times.
• Reactivity
• High reactivity may lead to rapid transformation; low reactivity may increase persistence.

These properties are often summarized in environmental risk assessments and used for classification (e.g. “persistent, bioaccumulative and toxic”, PBT).

Use Patterns and Technology

• Amount and frequency of use.
• Open vs. closed systems (e.g. sealed industrial reactors vs. open spraying).
• Quality of technical safety measures (containment, filters, wastewater treatment).
• Handling practices, maintenance, and training of personnel.

Even relatively hazardous chemicals can have low emissions if used in well-designed, closed systems; conversely, benign chemicals can contribute to environmental problems if enormous quantities are used diffusely.

Monitoring and Documentation of Releases

Understanding releases is a prerequisite for risk management.

Emission Inventories and Registers

• Compilation of data on quantities of pollutants released from different sectors (industry, transport, households, agriculture).
• Often broken down by substance and source category.
• Used for policy development, modeling of environmental concentrations, and international reporting.

Measurement and Estimation

• Direct measurements at point sources (stack measurements, wastewater analysis).
• Environmental monitoring of air, water, soil, and biota to detect and track contamination.
• Use of models to estimate emissions when direct measurement is not feasible (e.g. from millions of cars or households).

Prevention, Reduction, and Control of Releases

While detailed treatment of regulatory and technical measures belongs in other contexts, some core strategies for minimizing environmental release can be outlined.

Substitution and Product Design

• Replacement of particularly hazardous substances with less harmful alternatives.
• Design of chemicals and products that degrade more readily in the environment (“benign by design”).

Process and Equipment Optimization

• Closed systems to prevent escape of gases and liquids.
• Improved sealing of equipment and storage.
• Recovery and recycling of solvents and other valuable chemicals.

End-of-Pipe Technologies

• Exhaust gas treatment (filters, scrubbers, catalytic converters).
• Wastewater treatment (mechanical, chemical, biological processes).
• Secure waste disposal and controlled incineration for destruction of problematic substances.

Organizational Measures

• Training of personnel and users.
• Emergency plans and safety procedures to handle accidental releases.
• Clear labeling and information for users (e.g. on consumer products).

These approaches aim to minimize the release of chemicals at all stages, from production to disposal.

Summary

The release of chemicals into the environment is the result of many interconnected processes along a chemical’s life cycle. Emissions can originate from point, line, or diffuse sources and affect air, water, soil, and living organisms. The scale and impact of these releases depend on the properties of the substances, the way they are used, and the technical and organizational measures in place. Understanding pathways and patterns of release is essential for assessing environmental risks and for designing effective measures to protect ecosystems and human health.