Environmental Science - Pesticides and Fertilisers
Pesticides
Pesticides are substances used to prevent, destroy, or control pests, encompassing a broad range of chemical compositions.
Their effectiveness can lead to environmental pollution and risks to non-target species, including humans.
Properties of Pesticides
Specificity: Refers to how targeted a pesticide is towards a particular pest.
Non-specific pesticides can affect unintended organisms, reducing biodiversity and disrupting ecosystems.
High specificity is desirable to minimize unintended impacts.
Even highly specific pesticides can cause pollution if they affect closely related non-target species.
Persistence: The length of time a pesticide remains active in the environment before breaking down.
Highly persistent pesticides can remain in soil and water for years, leading to long-term exposure.
Extended presence can result in chronic pollution and make remediation difficult and costly.
Bioaccumulation: Occurs when a pesticide is absorbed by an organism faster than it can be metabolized or excreted.
Leads to pesticide buildup to toxic levels within an organism, particularly in fat tissue.
Fat-soluble and non-biodegradable pesticides are prone to bioaccumulation.
Biomagnification: Process that leads to increasingly higher concentrations of a pesticide in the tissues of organisms at each successive level of the food chain.
Predators eating contaminated prey concentrate pesticides.
Problematic with persistent, bioaccumulative pesticides, leading to high toxin levels in top predators, including humans.
Mobility: The ability of a pesticide to move within the environment.
Highly mobile pesticides can leach through soil into groundwater or run off into surface water, spreading contamination.
Can lead to pollution of waterways, affecting aquatic life and potentially entering human drinking water sources.
Pesticides that are persistent, mobile, non-specific, bioaccumulative, and biomagnifying can cause significant pollution problems.
Properties must be carefully considered to minimize environmental footprint and reduce pollution risk.
Effects of Pesticide Pollution
Pesticide pollution has direct and indirect effects on living organisms, ecosystems, and human health.
Direct Effects on Living Organisms
Toxicity to Non-Target Species: Pesticides can be toxic to beneficial insects (e.g., bees), aquatic invertebrates, birds, fish, and mammals.
Can lead to population declines and disruption of the food web.
Health Problems in Humans: Direct exposure can cause acute health problems like headaches, nausea, respiratory issues, and skin/eye irritation.
Chronic exposure is linked to serious health issues, including cancers, neurological disorders, reproductive issues, and endocrine disruption.
Poisoning of Wildlife: Animals may be poisoned by ingesting pesticide-contaminated food or water.
Birds may eat treated seeds; aquatic species may live in contaminated water.
Indirect Effects on Living Organisms
Ecosystem Imbalance: Pesticides can remove vital food sources, leading to imbalances in the ecosystem.
Killing insects can starve birds that feed on them.
Resistance: Pests can develop resistance to pesticides, requiring stronger chemicals.
Causes a cycle of increasing pesticide use and resistance, known as the "pesticide treadmill."
Bioaccumulation and Biomagnification: Persistent pesticides biomagnify up the food chain.
Can result in reproductive failures, immune system suppression, and hormonal disruptions in top predators.
Soil Fertility: Pesticides can affect soil microorganisms crucial for soil health and fertility.
Killing these organisms reduces soil biodiversity and nutrient cycling, leading to reliance on synthetic fertilizers.
Water Quality: Pesticide runoff contaminates streams, rivers, and groundwater.
Leads to algae blooms, oxygen depletion, and death of aquatic organisms.
Food Chain Disruption: Affecting one part of the food chain can have cascading effects on other organisms.
Reducing a plant population affects herbivores and their predators.
To mitigate these effects, pesticide use must be carefully managed using:
Integrated Pest Management (IPM) strategies utilize pesticides as a last resort, focusing on biological, physical, and cultural control methods.
Development of environmentally friendly pesticides that are less persistent, less bioaccumulative, and more specific to target pests.
Insecticides
Classified into various groups based on chemical structure and mode of action, each with specific impacts.
Organochlorines: (e.g., DDT, chlordane, aldrin) - Chlorinated hydrocarbons, widely banned due to environmental persistence and bioaccumulation.
Disrupt sodium/potassium balance in nerve cells.
Impacts:
Bioaccumulation and biomagnification, reaching toxic levels in top predators.
Endocrine disruption, affecting birds of prey and causing thinning eggshells.
Long-term environmental residues cause chronic exposure risks.
Organophosphates (OPs): (e.g., malathion, parathion, chlorpyrifos) - Inhibit acetylcholinesterase, causing nervous system failure.
Impacts:
Acute toxicity to a variety of organisms, including humans.
Significant environmental risks to aquatic life and beneficial insects.
Linked to short-term (headaches, dizziness) and long-term (neurological disorders, developmental problems) health issues.
Pyrethroids: (e.g., permethrin, cypermethrin) - Synthetic versions of natural insecticides that prolong the opening of sodium channels.
Impacts:
Highly toxic to fish and aquatic invertebrates, even at low concentrations.
Lower persistence than organochlorines but still pose risks due to high toxicity.
Effective against a variety of insects, often used in household pest control.
Neonicotinoids: (e.g., imidacloprid, clothianidin) - Affect the central nervous system, causing paralysis and death.
Systemic, meaning plants uptake the insecticide into their vascular system, expressing it in pollen, nectar, and dew.
Impacts:
Implicated in the decline of bees and other pollinators.
Affect insect behavior and reproductive success even at sub-lethal doses.
Water solubility leads to leaching into water bodies and potential aquatic ecosystem contamination.
Each group has faced regulatory scrutiny and restrictions. Responses include:
Banning and phasing out certain chemicals (e.g., organochlorines).
Developing safer application methods.
Searching for less harmful alternatives.
Promoting Integrated Pest Management (IPM) practices.
Controlling Pesticide Pollution
Reduce pesticide pollution to safeguard ecosystems, human health, and biodiversity.
Restrictions on Use: Regulatory bodies set restrictions or bans on harmful pesticides.
Persistent organic pollutants (POPs) are banned or restricted under international agreements like the Stockholm Convention.
Use of Non-persistent Pesticides: These break down quickly, reducing long-term contamination and bioaccumulation risks.
Use of More Specific Pesticides: Reduce impact on non-target species; minimize collateral damage to beneficial organisms.
Use of Systemic Pesticides: Can reduce the amount of pesticide needed; limit exposure to non-target organisms but present risks to pollinators if not used judiciously.
Application Timing: Applying pesticides when non-target organisms are less active can increase effectiveness and minimize exposure (e.g., spraying at dusk to reduce impact on bees).
Non-Pesticidal Techniques: Use non-chemical methods as a first line of defense.
Biological Control: Using natural predators, parasites, or pathogens.
Cultural Practices: Altering planting times, using trap crops, or rotating crops to disrupt pest life cycles.
Physical Controls: Using barriers, traps, or other mechanical means to remove or exclude pests.
Genetic Resistance: Developing crop varieties resistant to pests reduces the need for pesticides.
Education and Training: Educating farmers on proper pesticide use and alternative strategies.
Precision Agriculture: Using GPS and other technologies to apply pesticides only where and when needed.
Improved Formulation and Application Technology: Reduce drift and runoff; ensure pesticides are applied appropriately.
Monitoring and Enforcement: Monitor pesticide residues and enforce regulations.
These strategies represent a multi-faceted approach, emphasizing prevention, precision, and protection.
Inorganic Nutrients and Eutrophication
Inorganic nutrient pollution, primarily excessive nitrogen and phosphorus in waterways, disrupts aquatic ecosystems.
Sources of Inorganic Nutrients:
Agricultural Runoff: Fertilizers and manure run off fields into nearby water bodies.
Wastewater Discharges: Effluent from sewage treatment plants and septic systems contains high nutrient levels.
Industrial Discharges: Factories discharge wastewater containing nutrients.
Urban Runoff: Stormwater picks up fertilizers, pet waste, and detergents.
Atmospheric Deposition: Nitrogen compounds from burning fossil fuels return through precipitation.
Erosion and Sedimentation: Soil erosion carries nutrients into water bodies.
Environmental Issues Due to Excessive Nutrients:
Eutrophication: Excessive plant and algal growth deplete oxygen, leading to dead zones.
Harmful Algal Blooms (HABs): Some algae produce toxins.
Changes in Ecosystem Function: Species composition changes, decreasing biodiversity.
Cultural Eutrophication
Artificial enrichment of water bodies with nutrients (mainly phosphorus and nitrogen), contrasting with natural eutrophication.
Initial Effect: Increase in nutrient levels from agricultural runoff, sewage effluent, and fossil fuel emissions.
Address: Reducing nutrient runoff, improving wastewater treatment, managing stormwater runoff, and reducing emissions.
With more nutrients (especially phosphorus), algae and aquatic plants grow rapidly, leading to algal blooms.
Algae and plants die, bacteria decompose them, consuming dissolved oxygen which can lead to hypoxic conditions or dead zones.
Eutrophic conditions favor fast-growing species, leading to a loss of biodiversity.
Turbidity increases, reducing light penetration and affecting submerged vegetation.
Algal blooms release toxins and noxious compounds.
Disrupts the entire aquatic ecosystem, affecting food webs and habitat quality.
Impacts on Human Use: Compromises fishing, swimming, and recreational activities; increases water treatment costs.
Economic Costs: Reduces the commercial and recreational value of waterways, increases water treatment costs, and affects industries like fishing and tourism.
Addressing cultural eutrophication requires:
Nutrient Management: Implementing best practices in agriculture to reduce runoff.
Land Use Changes: Restoring wetlands and establishing buffer zones.
Policy and Regulation: Regulations on nutrient emissions and reducing the use of fertilizers and detergents with high phosphorus content.
Public Education: Raising awareness about the consequences of nutrient pollution.
Cultural eutrophication is preventable but requires concerted efforts.
The Effects of Nitrates
High levels of nitrates in drinking water can have adverse effects on human health.
Methemoglobinemia: Affects infants, reducing blood's ability to carry oxygen.
Pregnancy Complications: Associated with increased risks during pregnancy.
Cancer: Can be converted into nitrosamines, increasing cancer risk.
Thyroid Function: Interferes with iodide uptake by the thyroid gland.
Other Health Issues: Linked to diabetes.
Exposure related to contaminated drinking water from agricultural runoff, septic leachate, or improper waste disposal.
To mitigate, manage nitrogen-based fertilizers, maintain wastewater treatment, and monitor/treat drinking water.
Controlling Inorganic Nutrients
Control of nitrogen and phosphorus involves agricultural and waste management practices.
Reducing Use of Inorganic Fertilisers: Adopt better crop management techniques; precision farming.
Use of Slow-release Fertilisers: Release nutrients over a longer period.
Improved Manure Management: Careful handling and storage of livestock manure.
Crop Rotation and Reduced Ploughing: Reduce the need for chemical fertilisers, maintain soil structure, and reduce runoff.
Buffer Strips and Riparian Zones: Absorb nutrients before they enter a body of water; reduce soil erosion.
Cover Crops: Absorb residual soil nutrients and prevent washing away; add organic matter to the soil.
Phytoremediation: Use plants to absorb and assimilate nutrients from the soil.
Nutrient Management Plans: Applying agricultural nutrients more efficiently and sustainably.
Reducing Cultivation of High Nitrogen-requiring Crops: Opting for crops that require less nitrogen.
Integrating Livestock and Crop Production Systems: Using manure as fertiliser to recycle nutrients.
Use of Soluble Rapid-release Fertilisers: When applied correctly, can be quickly taken up by plants.
Reducing Reliance on Artificial Fertilisers: Encouraging the use of organic fertilisers, composting, and green manure.
Policy and Regulation: Regulate application rates of fertilisers and manage how and when they are applied.
These methods aim to maximise effectiveness and minimise environmental impact.
Iron(III) sulphate (ferric sulphate) is used in water treatment to remove phosphates that contribute to eutrophication.
Chemical Reaction: Reacts with phosphate ions to form insoluble iron(III) phosphate.
Precipitation: Forms precipitate that settles at the bottom of the water body.
Clarification: Water may be subject to clarification processes such as sedimentation or filtration, to remove the fine particles of iron(III) phosphate.
Reduced Algal Growth: By removing phosphates (limiting nutrient), the growth of algae is curtailed.
Restoration of Balance: Contributes to a healthier ecosystem and improves water quality.
Dredging: Physical method of removing sediments and nutrients from the bottom of lakes and rivers.
Removal of Nutrient-rich Sediments: Removes sediments rich in nitrogen and phosphorus.
Interruption of Internal Loading: Removes sediments that contribute to phosphorus release.
Restoration of Depth: Deeper waters can reduce nutrient availability to surface algae.
Habitat Alteration: Creates less favorable conditions for plants and algae.
Reduction in Anoxic Conditions: Reduces the occurrence of anoxic conditions that favor the release of phosphorus.
Both Iron(III) sulphate and dredging are strategies to manage inorganic nutrient levels, mitigate eutrophication, and improve water quality.
Nitrate Vulnerable Zones
Nitrate Vulnerable Zones (NVZs) are designated areas within EU countries at risk from agricultural nitrate pollution under the EU's Nitrates Directive (91/676/EEC).
NVZs are identified by member states as areas of land that drain into waters high in nitrates.
Farmers within NVZs must follow mandatory rules to reduce water pollution, including:
Limits on nitrogen fertilizer application.
Requirements for livestock manure storage.
Crop planning and management (using catch crops and cover crops).
Maintaining records of fertilizer/manure applications.
By designating NVZs and enforcing practices, the directive aims to control nitrate application and prevent waterway contamination.
Organic Nutrients
Organic nutrient pollution refers to the contamination of water bodies with organic matter from living organisms or byproducts.
Characterized by excessive amounts of organic nutrients (proteins, carbohydrates, fats).
Sources of Organic Nutrients:
Agricultural Runoff: Manure and bio-based fertilizers run off into streams, rivers, and lakes.
Urban Runoff: Stormwater collects organic waste (pet waste, yard clippings, garbage).
Wastewater Treatment Plants: Release organic materials into waterways.
Septic Systems: Inadequately treated effluent contaminates groundwater.
Food Processing Industries: Generate wastewater with high levels of organic matter.
Forestry and Land Clearing: Contribute to runoff of organic matter.
Aquaculture: Produces concentrated organic waste from feed and feces.
Landfills: Leachate contains high levels of organic matter.
Natural Sources: Dead and decaying matter contribute to the organic nutrient load.
Atmospheric Deposition: Organic compounds or precipitation collecting organic particulates from the air.
\figure 4 - Seagen being discharged into the ocean
The common factor among all these sources is that they contribute organic carbon to ecosystems.
This decomposition process can deplete oxygen levels in water, potentially leading to hypoxic conditions or dead zones where most aquatic life cannot survive.
Managing organic nutrient pollution requires a comprehensive approach:
Improving agricultural practices.
Enhancing wastewater treatment.
Promoting effective waste disposal.
Protecting natural buffers like wetlands.
Effects
Organic nutrient pollution has profound effects on ecosystems, particularly aquatic environments.
Deoxygenation: Reduction of dissolved oxygen in water bodies.
Hypoxic Zones: Inhospitable to many forms of aquatic life.
Anoxic Conditions: No life is sustainable; anaerobic bacteria produce harmful byproducts.
Pathogen Growth: Contains pathogens from agricultural runoff, wastewater, or urban sources.
Diseases: Can cause diseases in humans and animals (gastroenteritis, cholera).
Algal Blooms: High levels of nutrients can fuel the excessive growth of algae, including harmful algal blooms (HABs) that can produce toxins affecting aquatic life and human health.
Release of Inorganic Nutrients: Decomposition releases nitrogen and phosphorus.
Eutrophication: Rapid growth of algae and aquatic plants, leading to eutrophication, and creation of a cycle of depletion.
Biodiversity Loss: Altered nutrient levels shift species composition, reducing biodiversity.
Management Challenges:
Improved Waste Treatment: Enhancing efficiency of wastewater treatment plants.
Agricultural Best Practices: Proper manure management, buffer strips, and precision farming.
Urban Planning: Green infrastructure (permeable pavements, rain gardens) to mitigate stormwater runoff.
Public Education: Public awareness of the impacts of improper waste disposal.
Treatment of Organic Effluents
The treatment of organic effluents (wastewater treatment) involves several stages.
Pre-Treatment Methods: Remove large solids and materials.
Screening: Removes large debris.
Grit Removal: Settles out sand, grit, and sediment.
Flow Equalisation: Balances effluent flow.
Primary Treatment: Physical separation of solid and liquid wastes.
Sedimentation Tanks: Heavier solids settle; lighter materials float.
Secondary Treatment: Biological processes degrade organic matter.
Activated Sludge Process: Aerobic bacteria consume organic matter.
Trickling Filters: Wastewater sprayed over a bed of stones where bacteria consume organic matter.
Rotating Biological Contactors (RBCs): Bacteria grow on disks, promoting aerobic digestion.
Sludge Treatment: Treats sludge from primary and secondary treatment.
Thickening: Concentrates sludge.
Digestion: Stabilises sludge by breaking down organic matter which prevents pathogen from spreading.
Dewatering: Reduces water content.
\figure 6 - Typical drinking water treatment
\figure 7 - The water treatment process
Tertiary Treatment: Advanced treatment to remove remaining compounds, bacteria, viruses, and material.
Filtration: Removes residual particles.
Nutrient Removal: Removes nitrogen and phosphorus.
Disinfection: Kills remaining pathogens (chlorination, UV light, ozone).
Advanced Treatment: Additional treatments to meet standards.
Membrane Filtration: Removes very fine particles.
Ion Exchange: Removes inorganic compounds or softens water.
Carbon Adsorption: Removes odors, colors, and toxins.
After tertiary treatment, the water is safe for discharge or reuse.
The Impact of Weather on Sewage Systems
Weather-related fluctuations in sewage flow volume are due to rainwater infiltration and stormwater inflow.
Weather-related Fluctuations:
Infiltration: Groundwater seeps into sewage pipes, increasing flow after rainfall.
Inflow: Rainwater enters the sewage system through storm drains.
Stormwater Runoff: Stormwater channels into sewage pipes, increasing flow.
Types of Sewage Systems in the UK:
Combined Sewer Systems: Collect sewage and stormwater in a single pipe system. During heavy rainfall, systems become overwhelmed because it cannot handle both which potentially leads to combined sewer overflows (CSOs), where untreated sewage is discharged into nearby water bodies.
Separate Sewer Systems: Two separate networks (sewage and stormwater).
Sanitary Sewers: Carry only sewage.
Storm Sewers: Collect rainwater runoff.
Sustainable Urban Drainage Systems (SUDS): Manage runoff volumes and improve water quality naturally through permeable pavements, swales, and rain gardens so it can infiltrate into the ground naturally.
Management Strategies for Fluctuations:
Storage Tanks: Hold excess flow during peak times.
Real-Time Controls: Computer-controlled systems manage gates and pumps.
Green Infrastructure: Implementing green solutions helps to absorb rainwater to prevent flooding.
Managing fluctuations prevents environmental contamination from overflows and ensures treatment plants are not overwhelmed. \figure 5 - A vast water treatment station in Horsham, West Sussex, UK
Pesticides
Pesticides are substances used to control pests but can cause environmental pollution and harm non-target species.
Properties of Pesticides
Specificity: How targeted it is; high specificity minimizes unintended impacts.
Persistence: How long it remains active; high persistence causes long-term exposure.
Bioaccumulation: Absorbed faster than metabolized, leading to toxic buildup.
Biomagnification: Concentrations increase up the food chain, affecting top predators.
Mobility: Ability to move within the environment, causing widespread contamination.
Persistent, mobile, non-specific, bioaccumulative, and biomagnifying pesticides cause significant pollution.
Effects of Pesticide Pollution
Pesticide pollution affects organisms, ecosystems, and human health.
Direct Effects on Living Organisms
Toxicity to Non-Target Species: Harms beneficial insects, aquatic life, and mammals.
Health Problems in Humans: Causes acute and chronic health issues.
Poisoning of Wildlife: Animals ingest contaminated food or water.
Indirect Effects on Living Organisms
Ecosystem Imbalance: Removes food sources, disrupting the food web.
Resistance: Pests develop resistance, requiring stronger chemicals.
Bioaccumulation and Biomagnification: Impacts reproductive and immune systems.
Soil Fertility: Kills microorganisms, reducing soil health.
Water Quality: Runoff contaminates water, causing algae blooms and death of aquatic life.
Food Chain Disruption: Affects various organisms.
Mitigate effects through Integrated Pest Management (IPM) and environmentally friendly pesticides.
Insecticides
Insecticides are classified by chemical structure and action.
Organochlorines: Banned due to persistence and bioaccumulation; disrupt nerve cells.
Organophosphates (OPs): Inhibit acetylcholinesterase, causing nervous system failure.
Pyrethroids: Synthetic insecticides toxic to fish and aquatic invertebrates.
Neonicotinoids: Affect the central nervous system; linked to pollinator decline.
Responses include bans, safer methods, alternatives, and IPM.
Controlling Pesticide Pollution
Reduce pesticide pollution through various measures.
Restrictions on Use: Regulatory bans on harmful pesticides.
Use of Non-persistent/Specific Pesticides: Reduces contamination and impact.
Systemic Pesticides: Reduces pesticide amount but risks pollinators.
Application Timing: Minimizes exposure by applying when non-targets are less active.
Non-Pesticidal Techniques: Biological, cultural, and physical controls; genetic resistance; education; precision agriculture.
Inorganic Nutrients and Eutrophication
Inorganic nutrient pollution disrupts aquatic ecosystems.
Sources of Inorganic Nutrients: Agricultural, wastewater, industrial, urban runoff; atmospheric deposition; erosion.
Environmental Issues: Eutrophication, harmful algal blooms, changes in function.
Cultural Eutrophication
Artificial enrichment leading to algal blooms and oxygen depletion.
Address by reducing nutrient runoff, improving wastewater treatment, and public education.
The Effects of Nitrates
High nitrate levels in drinking water cause health issues.
Methemoglobinemia, Pregnancy Complications, Cancer, Thyroid Function
Controlling Inorganic Nutrients
Control involves agricultural and waste management.
Use slow-release fertilizers, improve manure management, crop rotation, buffer strips, cover crops, phytoremediation, and nutrient management plans.
Iron(III) sulphate removes phosphates and dredging removes nutrient-rich sediments.
Nitrate Vulnerable Zones
Areas at risk from agricultural nitrate pollution, following EU Nitrates Directive.
Organic Nutrients
Contamination with organic matter from living organisms.
Sources of Organic Nutrients: Agricultural, urban runoff, wastewater, septic systems, industries, forestry, aquaculture, landfills.
Effects:
Deoxygenation: Creates hypoxic zones.
Pathogen Growth: Causes diseases and algal blooms.
Release of Inorganic Nutrients: Leads to eutrophication.
Management Challenges: Improved waste treatment, agricultural practices, urban planning, public education.
Treatment of Organic Effluents
Involves pre-treatment, primary, secondary, sludge, tertiary, and advanced treatments.
The Impact of Weather on Sewage Systems
Weather affects sewage flow due to infiltration and inflow.
Types of Sewage Systems in the UK: Combined, separate, and SUDS.
Management Strategies: Storage tanks, real-time controls, green infrastructure.