Risk Analysis and Environmental Health Hazards

Transcription

1 Visualizing Environmental Science! Risk Analysis and Environmental Health Hazards Chapter 4 Chapter 7 [chapter opener image] Copyright

2 Four Steps for Risk Assessment Risk assessment: quanftafve and qualitafve characterizafon of risks in order to manage Hazard idenfficafon Can exposure have adverse health effects? Dose- response assessment What is the relafonship between the amount and the response? Exposure assessment How osen are individuals exposed? Risk characterizafon Leads to risk management

3 Environmental Health Hazards Toxicants Chemicals with adverse effects on health All chemicals are toxic if exposure is high enough Toxicology Studies the effects of toxicants on living organisms Evaluates the mechanisms that cause toxicity Develops ways to prevent or minimize adverse effects Handling and exposure guidelines

4 Environmental Health Hazards Epidemiology The study of how toxicants, biological agents (disease), and physical agents (accidents, radiafon) affect the health of human populafons Studies large groups of people and invesfgates range of causes and types of disease and injuries Toxicant exposure can be acute or chronic

5 Environmental Health Hazards Acute toxicity Immediate effects aser a single short period, high- level exposure Symptoms include dizziness, nausea, death Chronic toxicity Prolonged effects to long- term, low- level exposure Symptoms can mimic other chronic disease We know much less about chronic toxicity

6 Children and Chemical Exposure Children are more suscepfble than adults Weigh less than adults Interact more with their environment Undergoing growth and development Higher metabolic rate, requires more oxygen (increased suscepfbility to air pollufon) 1990 study in Los Angeles found that 80% of children who died for reasons other than respiratory disease had early stage lung disease

7 Determining Health Effects of Pollutants Toxicity determined by the dose that produced adverse effects Dose The amount of a toxicant that enters the body Response Type and amount of damage to a parfcular dose Lethal dose: causes death Sub- lethal dose: causes harm

8 Determining Health Effects of Pollutants Different doses of chemical administered to populafons of laboratory animals Data findings used to predict effects on humans The dose that is lethal to 50% of a populafon of test animals is called the LD 50 The smaller the LD 50, the more toxic the chemical

9 Determining the Health Effects of Pollutants The dose at which 50% of a populafon will exhibit the response under study (ED 50 ) Threshold level The maximum dose at which the toxicant has no measurable effect Doses lower than threshold level are considered safe This scienfst is measuring a toxicant in human blood serum

10 Dose- Response Curve Dose- response curve A graph that shows the effects of different doses on a populafon of test organisms Evidence suggests that there is not a safe dose for certain toxicants The figure on the left shows the response increases as the dose increases and harmful response is above threshold; on right, A has a lower ED50 than B, however B more toxic than A at lower doses

11 Cancer- Causing Substances Carcinogens are any substance that causes cancer Most common method of determining cancer- causing agent is to expose groups of laboratory animals to various doses and count how many animals develop cancer Indirect and uncertain Humans and laboratory animals may respond differently to chemical exposure Laboratory animals generally exposed to massive doses relafve to their body size Risk assessment assumes we can extrapolate from these experiments, determining expected cancer rates in humans and the safety of some chemicals assumpfons that may over or underesfmate a toxicant's danger EPA working with toxicologists to develop direct evidence of risk involved with exposure to low doses of cancer- causing chemicals

12 Risk Assessment of Chemical Mixtures Although humans are exposed to combinafons of chemical compounds in air, food and water, most studies are done on single chemicals Mixtures of chemicals increase level of complexity in risk assessment Too many chemical mixtures to evaluate Chemical mixtures interact by one of three ways: addifvity, synergy, or antagonism AddiFvity: the addifve effect of each component of the mixture AddiFvity is generally used in order to asses the risk for chemical mixtures Synergy: the mixture has a greater combined effect than the chemicals individually AntagonisFc: mixture has a smaller combined effect than the chemicals individually

13 The PrecauEonary Principle The idea that we should not adopt a new technology, pracfce, or material unfl it is demonstrated that: The risks are small The benefits outweigh the risks Puts the burden of proof onto the developers An ounce of prevenfon is worth a pound of cure These city kids are probably exposed to lead in the soil (from leaded gasoline)

14 The PrecauEonary Principle: Common Sense? There is also controversy ScienFsts feel it endorses the making of decisions without the input of science The EU (European Union) banned beef from U.S. and Canada because of the use of hormones to make cable grow faster The EU uses precaufonary principle with respect to GMOs (genefcally modified organisms) PrecauFonary principle or economic protecfonism?