2 dose-response relationships Flashcards
what are the classifications of toxicity?
-direct: results from toxic agent acting more or less directly on the organisms
-indirect: results from the influence of changes in the environment, acting indirectly on the organisms
who was Paracelsus?
16th century physician
-the father of toxicology
-“all substances are poisons. There is none which is not a poison. The right dose differentiates a poison from a remedy”
-the dose makes the poison
what are the principles of toxicology?
-experimentation/testing is essential in the examination of responses to chemicals
-one should make a distinction between the therapeutic and toxic properties of chemicals
-these properties are sometimes but not always indistinguishable except by dose
-toxic effects are dose/concentration dependent, and the effects must be quantifiable
what is NOEC and LOEC?
-NOEC= no observed effects concentration (safe level)
-LOEC= lowest observable effects concentration (threshold)
what is MATC?
maximum acceptable toxic concentration
-MATC=(NOEC+LOEC)/2
-often used to reduce toxic level of exposure to contaminants
toxicity can be expressed in different ways:
-LC50 or LD50: concentration or dose that causes 50% mortality under a defined test condition
-ED50: concentration that elicits 50% of expected effect/response (half of maximal effect) under a defined test condition
-IC50: concentration that reduces the normal response of a parameter by 50%
what are common units of dose or exposure?
ppm=parts per million
-mg/kg in weight/weight (e.g. dose/body weight)
-mg/L in weight/volume liquid
ppb=parts per billion
-μg/kg in weight/weight
-μg/L in weight/liquid
toxicity can be expressed in ___________
different ways (reference doses or concentrations)
how would you compare the toxicity of compounds 1 and 2, or compounds 1 and 3?
what are some other types of dose-response curves?
what is the range of effects of a toxicant on a population?
what are the different types of toxicity tests?
-acute
-chronic
-microcosms/mesocosms
what is the acute toxicity tests?
-short-term, exposure to high-dose, single species
-standard times (e.g. 48, 96-hr exposures)
-adjust for species life-span (e.g. 24 hrs to 2 weeks)
-common test endpoint: mortality
-aquatic tests: static, static renewal and flow-through
what is the chronic toxicity tests?
-long-term, exposure to low or sub-lethal dose, single species
-standard exposure time: 21 days to several years depending on organism tested
-common test endpoints: growth and reproductive fitness
-several other specific endpoints are also considered particularly in higher vertebrates (e.g. endocrine malfunction, carcinogenesis)
what is the relationship between acute and chronic toxicity?
acute to chronic ratio (ACR)= Acute LC50/MATC
-ACR is used to gauge the concentration of a toxicant that may cause chronic toxicity to exposed organisms
what is the microcosm/mesocosm toxicity tests?
-two or more species, single or multiple toxicants
-more environmentally realistic
-allows to study interspecific and community level interactions
-looked at for 21 days of exposure
-looked at accumulation and sub-lethal effects (reproductive failure)
what are the differences in lab studies and field studies?
lab studies: all test conditions are controlled and constant, only 1 variable is changing (dose/concentration)
field studies:
-highly dynamic environments (ex: food, predation, temperature, weather)
-species that are more abundant are more tolerant to toxicant
-expensive, time consuming and need more man power
-can be very complex
what are commonly used organisms for soil toxicity tests?
-earthworms (e.g. eisenia andrei)
-springtail (e.g. folsomia candida)
what are commonly used organisms for aquatic toxicity tests?
daphnia
-are crustaceans (with transparent shell)
-become sexually mature at 7 days
-shed every 3 days and produce eggs
what is the significance of using three different types of organisms?
-occupy different trophic levels
-helps us understand food chain toxicity in nature
what is some species sensitivity distribution?
what is the toxicity of pollutant mixtures (toxic unit approach)?
-additive (2+2=4)
-synergistic (greater than additive) (2+2=10)
-antagonistic (less than additive) (2+2=1)
toxic unit=reference dose (can be anything, LC50, LC10, LD30, etc)
-synergistic=one can effect the metabolic pathway of another to optimize effects
what is the evaluation of mixture toxicity (TU approach)?
LC50 of toxicant A=10 ppm (1 TU of A)
LC50 of toxicant B=50 ppm (1 TU of B)
