Lecture 1
3 parts: environmental chemistry (sources, reactions, transport and fate of
chemical species in air, water and soil) - toxicology (harmful effects of
chemical, physical and biological agents on living organisms) - epidemiology
(branch of epidemiology concerned with determining how environmental
exposures impact human health).
Case study: a problem related to environmental chemistry and health → you
have to formulate an advice for humans → it is a self-study (have to do it by
yourself) → 2 components: output presentation (15%) and written report (35%).
Chemicals in the environment: from anthropogenic and
geogenic or natural sources → the contaminants will
be cycling in the environment → these compartments
are interlinked (picture left).
→ important to understand the transportation of
chemicals to understand its impact on health.
Behaviour and risk of chemicals depends on the
chemical speciation.
- Speciation of an element: distribution of an
element amongst defined chemical species in a system.
- Chemical species: a specific form of a chemical
element, defined as its complex structure or oxidation state.
- Chemical speciation helps understand mobility, bioavailability and toxicity of substances.
→ examples: chromium (Cr) has different oxidation states → most
common: (1) Cr(III) as cation Cr3+, (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.
→ example: mercury (Hg) is a highly toxic heavy metal → especially organo-mercury compounds
bioaccumulate in aquatic environments → consumption of fish can cause mercury toxicity →
BUT, metallic and inorganic mercury species are less dangerous → FEX. mercury (Hg0) for tooth
fillings and jewelry containing mineral cinnabar (HgS) →
because they are poorly soluble and absorbed by a much
smaller extent.
Conclusion: chemical speciation of substances in the
environment is (a) complex and (b) the result of many
simultaneous physical, chemical
and biological processes.
Chemical speciation of metals:
picture right → metals behave
differently at different stages.
Uptake = how metal ions enter the cellular material.
Absorption = 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 aqueous solution combine to form an insoluble ionic
solid.
,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: based on conservation of matter = sum of all species of a
certain element must be equal to the amount of the element delivered to the
solution → include all relevant species, they add up to the total amount in the
system.
→ example of mass law equation.
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
plays a central role in
understanding speciation in
environmental systems → most
equilibrium reactions involve the
free concentration → 2 ways of
calculating.
Reactive soil surfaces: in the environment we find reactive solids with a large surface area,
with the ability to bind solutes → FEX. organic matter, clay and metal(hydr)oxides.
Absorption: solution with a high affinity for surfaces are often primarily absorbed →
sorption isotherms describe the equilibrium between the absorbed concentration (Q in
mol/kg) and the solution concentration (C in mol/L) → for transport, sorption is a
process of major importance → retardation = the velocity of solute in water → the velocity of
how much a solute is moving slower → how much slower a solute is going (factor larger than 1).
Pictures below: explain absorption and retardation.
, Bioavailability = the degree to which chemicals may be absorbed or 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 → chemical
speciation helps understand the mobility, bioavailability and toxicity of substances.
→ many organisms predominantly take up molecules and ions from the aqueous phase →
assumption: only dissolved species are directly bioavailable, BUT adsorption of the dissolved
species/solutes may occur → however, if sorption equilibrium is preserved, the solution
concentration will be replenished through desorption and are referred to as potentially
bioavailable.
Risk evaluation environmental contamination: to evaluate the necessity to remediate
environmental contamination, various risks are evaluated: (a) threat to human health, (b) threat
to ecosystem health, (c) threat of spreading → are influenced by speciation.
→ the national institute for public health and the environment (RIVM) develops methods, models
and instruments to perform risk assessments of contaminated sites.
Soil contamination in 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 → less available to be taken up by the plant.
→ the pH is also important → at a low pH, the grass suffers from more copper than at a high pH
(because there is more copper available for the plant to take up, so growth decreases over time).
Dutch regulation: the concepts of chemical speciation and bioavailability are incorporated in
Dutch regulation on environmental contamination, BUT to a limited extent
→ examples: (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 (on the safe side), it is based on “total
amounts” rather than “reactive amounts” or “potentially available amounts” of contaminants.
→ drawback: potentially substantial costs when there are no actual threat risks.
Lecture 2
Examples of toxicology: PFAS chemicals which contaminate plastic food containers → firponil in
eggs → chromium 6 in paint which was used without protection → crumb rubber in soccer
fields, but people, especially children, received too much chemicals from this and could get
cancer → high levels in carcinogen in paracetamol → microplastics form a
health risk → steel industry causes high pollution.
Toxicology = study of adverse effects of chemical, physical or biological
agents on living organisms → exposure to toxic chemicals → is it safe to use
