BESC 201 10 7 2013 Lecture 17 Outline of Last Lecture I Toxicity Outline of Current Lecture II Studying Effects of Hazards III Risk Assessment and Risk Management Current Lecture 10 9 2013 Studying Effects of Hazards Wildlife studies integrate work in the field and lab Work in the field with animals to take measurements documents patterns and generate hypotheses before heading to the laboratory to run controlled manipulative experiments to test their hypotheses Human studies rely on case histories epidemiology and animal testing Epidemiological Studies large scale comparisons among groups of people usually contrasting a group known to have been exposed to some hazard and a group that has not Epidemiologists track the fate of all people in the study for a long period of time and measure the rate at which deaths cancers or other health problems occur in each group Epidemiological studies measure a statistical association between a health hazard and an effect but they do not confirm that the hazard causes the effect Dose response analysis is a mainstay of toxicology Dose Response Analysis scientists quantify the toxicity of a substance by measuring the strength of its effects or the number of animals affected at different doses Dose the amount of substance the test animal receives Response the type or magnitude of negative effects the animal exhibits The response is generally quantified by measuring the proportion of animals exhibiting negative affects Dose Response Curve the data are plotted on a graph with dose on the x axis and response on the y axis LD 50 lethal dose for 50 of individuals A high LD 50 indicates low toxicity for substance and a low LD 50 indicates high toxicity ED 50 the level of toxicant at which 50 of a population of test animals is affected in some other way Threshold some substances elicit effects only above a certain dose These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Examples a body s organs can fully metabolize or excrete a toxicant at low doses but become overwhelmed at higher concentrations cells can repair damage to their DNA only up to a certain point Sometimes a response may decrease as a dose increases Dose response curves are U shaped J shaped or shaped like an inverted U often occur with endocrine disruptors Estimating effects on humans often requires extrapolation extending the dose response curves beyond the doses tested with lab animals introduces uncertainty into the interpretation of what doses are safe for people Mixes may be more than the sum of their parts Chemical substances when mixed may act together in ways that cannot be predicted from the effects of each in isolation Synergistic Effects interactive impacts that are greater than the simple sum of their constituent effects In toxicology the complex experimental designs required to test interactions and the sheer number of chemical combinations have meant that single substance tests have received priority Endocrine disruption poses challenges for toxicology Because so many novel synthetic chemicals exist in very low concentrations over wide areas many scientists suspect that we may have underestimated the dangers of compounds that exert impacts at low concentrations There is debate partly because of the scientific uncertainty inherent in any emerging field of study but also because of the economic value of the chemicals being tested Risk Assessment and Risk Management We express risk in terms of probability Exposure to an environment health threat does not invariably produce a given effect Rather it causes some probability of harm a statistical chance that damage will result A scientist must also know the chance that one will encounter it the frequency with which one may encounter it the amount of substance or degree of threat to which one is exposed and one s sensitivity to the threat Our perception of risk may not match reality The difference between perception and reality stems from the fact that we feel more at risk when we are not controlling a situation and more safe when we are at the wheel regardless of the actual risk involved Risk assessment analyses risk quantitatively Risk assessment the quantitative measurement of risk and the comparison of risks involved in different activities or substances together Risk assessment is a way to identify and outline problems The first steps involve the scientific study of toxicity Subsequent steps involve assessing the individual s or population s likely extent of exposure to the substance Risk management combines science and other social factors Risk management consists of decisions and strategies to minimize risk Federal agencies Environmental Protection Agency EPA the Centers for Disease Control and Prevention CDC and the Food and Drug Administration FDA Scientific assessments of risk are considered in light of economic social and political needs Economic benefits are generally known easily quantified and of a discrete and stable amount whereas health risks are hard to measure probabilities often involving a small percentage of people likely to suffer greatly and a large majority likely to experience little effect Two approaches exist for determining safety One approach is to assume that substances are harmless until shown to be harmful innocentuntil proven guilty Virtue of facilitating technological innovation and economic activity disadvantage of putting into wide use some substances that may later turn out to be dangerous Other approach is to assume that substances are harmful until shown the be harmless precautionary principle Enable us to identify troublesome toxicants before they are released into the environment but it may also impede the pace of technological and economic advance Philosophical approaches are reflected in policy FDA monitors foods and food additives cosmetics drugs and medical devices EPA regulates pesticides Occupational Safety and Health Administration OSHA regulates workplace hazards Synthetic chemicals not covered by other laws are regulated by the EPA under the 1976 Toxic Substances Control Act TSCA EPA regulation is only partly effective Toxic Substances Control Act TSCA directs the EPA to monitor the roughly 83 000 industrial chemicals manufactured in or imported into the United States Public health advocates vies TSCA too weak they note that the screening required of industry is minimal and that to