toxicology and industrial hygiene the chemical engineers must be knowledgeable about the way...
TRANSCRIPT
Toxicology and Industrial Hygiene
The chemical engineers must be knowledgeable about
• The way toxicants enter biological organisms (T);• The ways toxicants are eliminated from biological
organisms (T);• The effects of toxicants on biological organisms
(T);• Methods to prevent or reduce the entry of
toxicants into biological organisms (H).
Poison
“All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy.”
by Paracesus
“There are no harmless substances, only harmless ways of using substances.”
More Definitions• Toxicant: A toxicant can be a chemical or
physical agent, including dusts, fibers, noises and radiation.
• Toxicity: Toxicity is the a property of the toxicant describing its effects on biological organisms.
• Toxicology: The qualitative and quantitative study of the adverse effects of toxicants on biological organisms.
How toxicants enter biological organisms?
• Ingestion – via mouth into stomach;
• Inhalation – via mouth or nose into lungs;
• Injection – via cuts into skin;
• Dermal Absorption – through skin membrane.
Methods for Control
• Ingestion: enforcement of rules on eating, drinking and smoking.
• Inhalation: ventilation, respirators, hoods and other personal protection equipment.
• Injection: proper protective clothing.
• Dermal absorption: proper protective clothing.
How toxicants are eliminated from biological organisms?
• Excretion: through the kidney, liver, lungs or others. Kidneys are the dominant means.
• Detoxification: by changing the chemical into something less harmful by bio-transformation. Liver is the dominant organ.
• Storage: in the fatty tissue.
Toxic effects that are irreversible
• Carcinogen causes cancer.
• Mutagen causes chromosome damage.
• Reproductive hazard causes damage to reproductive system.
• Teratogen causes birth defects.
Effects may or may not be reversible
• Dermatotoxic affects skin.
• Hemotoxic affects blood.
• Hepatotoxic affects liver.
• Nephrotoxic affects kidneys.
• Neurotoxic affects nervous system.
• Pulmonotoxic affects lungs.
Toxicological Studies
A major objective is to quantify the effects of the suspected toxicant on a targeted organism. For most studies, small animals (mice, rabbits or guinea pigs) are used. The following items must be identified in advance: (1) the toxicant, (2) the target or test organ, (3) the effect or response to be monitored, (4) the dose range and (5) the test period.
The Dose Units
• For substance delivered directly into the organism by ingestion or injection, the dose is measured in mg of agent per kg of body weight.
• For gaseous airborne substances, the dose is measured in either ppm or mg of agent per cubic meter of air (mg/m^3).
• For air borne particulates, the dose is measured in mg of agent per cubic meter of air (mg/m^3) or millions of particles per cubic foot (MPPCF).
Dose Versus Response
The lethal dose curve in Figure 2-3 is a curve of probability of lethality (P) vs. logarithm of the dose (V). This curve is usually sigmoidal.
For comparison purposes, the dose that result in 50% lethality is often reported. This is called the dose.50LD
The Probit VariableProbit is the abbreviation of Probability Unit. The probit variable Y is chosen as a normally distributed randomvariable with mean 5 and variance 1. Thus, a given lethalityprobability can be expressed with Y according to
dueYPY
u
52
2
2
1)(
(See Table 2-1, Figure 2-4). Note that a Y can be determined from a given P.
The Probit Transformation
The probit relationship transforms the sigmoid shape of the normal response vs dose curve into a straight line when plotted using a linear probit scale (Figure 2-5).
Standard curve fitting techniques are used to determine the best fit straight line, i.e.
lnY a b V
The Causative Factor (Dose)• Continuous Discharge: , where C is conc
entration in ppm, t is the exposure timein minutes, a, b and n are regression constants (listed in Table 2-2).
• Instantaneous Discharge: , where the subscript i is used to indicate the i-th time interval.
• Other (see Table 2-3)
i
m
iitCV
1
nV C t