Environmental Forensics

Question 1

Polychlorinated biphenyls (PCBs) are

Answer 1

Man made chemicals.
They have 2–10 chlorine atoms attached to the biphenyl molecule.
Used in hydraulic fluids, casting wax, compressors, heat transfer systems, plasticizers, pigments, adhesives, liquid cooled electric motors, fluorescent light.
Relatively insoluble in water.
Very stable at high temperature and pressure, resistant to acids and bases.
Their degradation include hydrogen chloride, polychlorinated dioxins, and polychlorinated furans

Question 2

PCBs in Environment

Answer 2

Exist due to human activities
PCBs are also prone to long-range atmospheric transport and deposition.
PCBs persist in the environment for decades.
PCBs bio-accumulate up the food chain in body fat.

Question 3

Toxicity of PCBs

Answer 3

PCBs are absorbed from the gastrointestinal tract, through the skin or by inhalation.
The initial uptake of PCBs is by the liver and muscle then they are redistributed into adipose tissue
PCB metabolites accumulate in the lung
PCB are carcinogenic
Sulfur-containing and hydroxylated products are the major metabolites.

Question 4

Polycyclic aromatic hydrocarbons (PAHs)

Answer 4

A class of organic compounds consisting of two to six fused benzene rings.
Mostly colorless, white, or pale yellow solids.
Have high melting and boiling points, low vapor pressure, and very low water solubility. PAHs are very soluble in organic solvents because they are highly lipophilic.
PAHs are associated with many industrial activities (e.g., refineries, smelters, gas plants, coal-fired power plants, wastewater treatment, storm water runoff)
PAHs also have natural origins (oil seeps, erosion, volcanic eruptions, vegetative decay)

Question 5

Toxicity of PAHs

Answer 5

PAHs are persistent in the environment, and can be bio-accumulated.
Toxicity is due to the interference of these compounds with the function the enzymes in the body.
PAHs are also potent immune-suppressants.
PAHs can cause carcinogenic and mutagenic effects
Toxicity of PAHs increase in the presence of ultraviolet light

Question 6

Pesticides

Answer 6

Most pesticides are non polar and hydrophobic.
The non polar pesticides tend to deposit in soils and sediments of organic matter.
Degrade in the environment to other toxic compounds under the effect of temperature, light, pH and organisms.
Chemical degradation occurs by one of 3 reactions; oxidation, reduction, and hydrolysis.
Three families of pesticides, organochlorine, organophosphorus (OPs), and carbamates

Question 7

Organochlorine pesticides

Answer 7

Organic compounds with five or more chlorine atoms
Disrupt the nervous system function, leading to convulsions and paralysis
Have a long-term residual effect in the environment since they are resistant to most chemical and microbial degradations

Question 8

Organophosphorous pesticides

Answer 8

Contain a phosphate group in their molecular structure
Work as cholinesterase inhibitors leading to a permanent overlay of acetylcholine neurotransmitter
As a result, nervous impulses fail to move causing paralysis and death.
Decompose in the environment by various chemical and biological reactions

Question 9

Carbamates

Answer 9

Derived from carbamic acid
They inhibit the cholinesterase enzyme

Question 10

Pyrethroids

Answer 10

Synthetic analogues of the naturally occurring pyrethrins
They have fast nock down effect against pests and low toxicity to mammals
They degrade photochemically at a very fast rate

Question 11

Dioxins

Answer 11

The basic structure is a dibenzo-p-dioxin (DD) molecule.
Colorless solids or crystals. Low solubility in water and a low volatility.
Environmentally and biologically persistent
Found in all humans, with higher levels commonly found in persons living in more industrialized countries

Question 12

Oil spills

Answer 12

Cause extensive damage to marine life, and natural resources.
Compounds of interest in the composition of oils include, straight chain hydrocarbons (normal alkane series), branched chain hydrocarbons and aromatics
Biomarkers
isoprenes (pristane and phytane)
terpanes and steranes
napthalenes
Profiling of the above components is carried out for comparison purposes

Question 13

Identification of oil spills

Answer 13

The major hydrocarbon groups in oils are :
C8–C40 n-alkanes
The volatile BTEX (benzene, toluene, ethylbenzene)
Alkylated benzenes (C3 to C5 benzenes)
Pristane and phytane.

Question 14

Analysis

Answer 14

Requires efficient sample pre-treatment to extract the compounds from complex matrices (air, water, soil, sediments, biological fluids)
Chromatography (GC, HPLC), is applied to separate and detect each compound
UV and FID are used as universal detectors for PAHs, dioxins, oil spills
Fluorescence detectors are selective towards carbamates
Nitrogen-phosphorous detector (NPD) is selective towards organophosphorus pesticides
Electron capture detector (ECD) is selective towards halogenated compounds such as organochlorines pesticides, PCBs, dioxins
Mass and IR detectors are fingerprint detectors

Question 15

Pattern recognition of oil spills

Answer 15

Pattern recognition of complex chromatograms is sufficient to identify oil or fuel or their residues.
Chromatograms provide a distribution pattern of petroleum hydrocarbons
Small clusters of peaks represent compounds of similar chemical composition and boiling points.
Chromatograms also provide information on the biodegradation indicators (n-C17/pristane , n-C18/phytane).

Question 16

Effects of weathering on an oil spill

Answer 16

For lightly weathered oils, significant losses of light n-alkanes occur.
Rapid loss of the BTEX occur.
At 20-25% weathering, the BTEX are completely lost.
In heavily weathered oils, the n-alkanes, and isoprenoids are completely lost.