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Summary lectures and videos Environmental Chemistry and Health (GEO3-2119)
Summary of all the lectures and lecture videos for the course Environmental Chemistry and Health.
[Meer zien]Voorbeeld 3 van de 29 pagina's
Voorbeeld 3 van de 29 pagina's
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Voorbeeld van de inhoud
Environmental Chemistry1. Introduction
Environmental chemistry = sources, reactions, transport and fate of chemical species in air,
water and soil → sources; anthropogenic, geogenic and natural.
Concepts:
Uptake how metal ions enter cellular material.
Adsorption adhesion of metal ions onto a surface.
Dissociation a compound that breaks into its component ions.
Complexation a metal atom or ion bonded to one or more ligands
(ions or molecules that contain one or more pairs of
electrons that can be shared with FEX. metals).
Precipitation when cations and anions in an aqueous solution
combine to form an insoluble ionic solid.
Behaviour and risk of chemicals depends on the chemical speciation = is (a) complex and (b) the
result of many simultaneous physical, chemical and biological processes.
- Speciation of an element: distribution of an
element amongst defined chemical species in a system.
- Chemical species: a specific form of a chemical
element (its complex structure or oxidation state).
→ helps to understand mobility, bioavailability and
toxicity of substances.
→ FEX. chromium (Cr) has different oxidation states →
most common: (1) Cr(III) as cation Cr3+ and (2) Cr(VI) as
anion chromate (CrO42-) → due to different nature of
the charge the chromium
species behave different in the environment and pose different risks.
→ FEX. mercury (Hg) is a highly toxic heavy metal → consumption of fish
can cause mercury toxicity → BUT, metallic and inorganic mercury
species are less dangerous, such as mercury (Hg0) for tooth fillings and
jewelry containing mineral cinnabar (HgS) (they are poorly soluble and
absorbed by a much smaller extent).
Chemical speciation of metals (picture right): metals behave differently at
different stages → changes in speciation can be described through 2 different approaches:
1. Thermodynamics: for reactions that are at equilibrium ∆G=0 (Gabbs free energy) →
speciation can be described using mass law and mass balance equations.
a. at equilibrium: rateforward = ratereverse →
𝑐 𝑑
[𝐶] [𝐷]
b. mass law equation: Kw = [OH-][H+] = 10-14 → aA + bB ↔ cC + dD → K = 𝑎 𝑏
[𝐴] [𝐵]
c. mass balance equation: conservation of matter = sum
of all species of a certain element must be equal to the amount of the
element delivered to the solution → includes all relevant species,
they add up to the total amount in the system → example of mass law
equation in picture left.
, 2. Kinetic description: rate
law equations (A → B) →
zero, first and second
order (pictures right).
In an environmental system, a
single element participates in
many reactions that form a
complex reaction network → free
concentration = understanding speciation in environmental systems → most equilibrium
reactions involve the free concentration → 2 ways of calculating:
1. Solubility of a miner: Al(OH)3 (s) ↔ Al3+ (aq) + 3OH- (aq) → for a given pH and solubility
product (Ksp) the free concentration is calculated from the mass law equation → the
concentration of other chemical species (FEX. Al(OH)2+ (aq)) can be calculated by using a
mass law equation again → Al3+ (aq) + OH- (aq) ↔ Al(OH)2+ (aq).
2. Total amount of the element distributed over a number of species: mass
balance equation is used → [Me]T = [Men+(aq)] + (MeDOM (aq)] + [MeCln+1 (aq)] +
[MeOHn-1 (aq)] → the concentrations of all free concentrations are expressed in
terms of the free concentration by using mass law equations, such as
[MeOHn-1 (aq)] = K · [Men+(aq)] · [OH- (aq)] (picture left).
In the environment there are reactive solids with a large surface area, with the ability to
bind solutes → FEX. organic matter, clay and metal(hydr)oxides.
Adsorption = solutions with a high affinity for surfaces are often adsorbed (more particles
means more solute is sorbed) → sorption isotherms = the equilibrium between the
adsorbed concentration (Q in mol/kg) and the solution concentration (C in mol/L) →
important process for transport → sorption isotherms can be different depending on the solute
and sorbent (picture right):
- Linear adsorption isotherms: Q = KdCL
𝐾𝐶𝐿
- Langmuir adsorption isotherms: Q = Qmax 1+𝐾𝐶𝐿
→ takes into account that sorption can
have a maximum as a result of a limited number of available sorption sites.
→ sorption depends on: (a) K = the affinity constant of a solute for the solid phase
(affinity for the solid phase) → partition coefficient for linear sorption (C and Q
remain constant). (b) amount of solid phase per amount of solution (expressed in
suspension density or solid-to-solid ratio (SSR) in kg/L).
→ mass balance equation (per volume): CT = CL + CS (T = total, L = liquid, S = solid) →
CS = Q · SSR → linear sorption; CS = K · CL · SSR → so, CT = CL · (1 + K · SSR).
Retardation = the velocity of solute in water (velocity of how much a solute is moving slower,
factor larger than 1) → in groundwater, mainly dissolved species are transported → adsorption
limits the dissolved concentration, so transport and adsorption are related.
→ for a porous medium: SSR = ρ𝑏/θ → ρ𝑏 = bulk density of the sediment (kg/L), θ = pore
volume (L/L) → CT = CL (1 + K · ρ𝑏/θ) → (1 + K · ρ𝑏/θ) = the retardation factor (R) = the
factor by which a solute travels slower than water.
Bioavailability = the degree to which chemicals are absorbed/metabolised by human or
ecological receptors or are available for interaction with biological systems → related to chemical
speciation → not all species of a certain chemical can be taken up.
, → many organisms take up molecules and ions from the aqueous phase → if the sorption
equilibrium is preserved, the solution concentration is replenished and potentially bioavailable.
Risk evaluation environmental contamination: evaluate threat… (a) to human health, (b) to
ecosystem health, (c) of spreading → are influenced by speciation.
Soil contamination NL: 250.000 locations are contaminated and 1518 require urgent action →
pressure on (a) spatial use, (b) below ground building activities, (c) heat-cold storage in the
subsurface, (d) groundwater use for drinking water.
→ soil texture influences metal toxicity → clay has a higher cation exchange capacity (CEC) and
binds Cu more strongly, so there is less available to be taken up by plants → pH: at a low pH, the
grass suffers from more Cu than at a high pH (because there is more Cu available for the plant to
take up, growth decreases over time).
Dutch regulation regarding chemical speciation and bioavailability: FEX.
(a) correction of the intervention value for lutum and organic matter content of a soil.
(b) distinction between chromium (III) and chromium (VI).
(c) distinction between organic and inorganic mercury.
→ Dutch regulation is conservative (they avoid risks) and it is based on total amounts rather than
reactive amounts or potentially available amounts of contaminants.
2. Urban evironments and chemistry
Urbanisation = process by which an increasing percentage of a country’s population comes to
live in towns and cities → drastic change in the last century → causes:
- Migration from villages to cities → push factors: food security, low income, high
population growth, but low resources, lack of resources for agriculture → pull factors:
better accommodation facilities, lots of jobs, good healthcare, education opportunities.
- Natural increase due to (a) migration of young adults, (b) more births and (c) mortality
rates are lower than birth rates.
Different types of pollution in urban areas:
- Water pollution: presence of excessive amounts of
harmful pollutants → anthropogenic; chemicals, sewage, plastic,
radioactive waste, oil → natural; volcanoes, foods, animal waste,
algae → unsafe water kills a lot of people.
→ point sources: pollutants derived from
a single source (FEX. leaking septic tank
systems, storage tanks and lagoons,
water discharge by industries) → non-point source: pollutants derived
from multiple sources (FEX. urban streets containing chemicals and gas,
pesticides and fertilisers, rain containing pollutants).
→ types of water pollution: (a) domestic sewage (human excreta, kitchen
waste, soap, detergents). (b) industrial waste (acid, alkali, chemicals, oil,
pharmaceuticals, persticides, insecticides). (c) other polluting agents
(hospital, agricultural, radioactive waste).
→ water pollutants in urban areas:
Inorganic heavy metal pollution = any metallic element that has a relatively high density
pollutants and is toxic and poisonous at low concentrations → sources: mining, smelting, corrosion,
industrial smoke, waste disposal → can cause bioaccumulation and oxidation → arsenic
pollution: comes from industry, agriculture and other sources, causes skin cancer, can be
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