Bioaccumulation and Biomagnification
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AP Environmental Science › Bioaccumulation and Biomagnification
A single largemouth bass in a reservoir is tested for mercury (methylmercury) each year. Its mercury concentration rises from 0.3 ppm at age 1 to 0.7 ppm at age 3 to 1.2 ppm at age 6, even though the water concentration stays very low and stable. Which process is best illustrated?
Biomagnification because mercury concentration is increasing from water to the bass over time.
Bioaccumulation within the bass over time as mercury is retained faster than it is eliminated.
Bioaccumulation because mercury is rapidly metabolized and excreted, preventing buildup.
Biomagnification because mercury concentration always decreases at higher trophic levels.
Explanation
Bioaccumulation is the gradual accumulation of a substance like mercury in an individual organism's tissues over its lifetime, where the rate of intake exceeds elimination. Biomagnification involves the amplification of toxin concentrations across trophic levels in a food web, as higher-level consumers eat many lower-level organisms. This scenario shows a single bass with increasing mercury levels over years (0.3 ppm to 1.2 ppm) despite stable water concentrations, which exemplifies bioaccumulation as the fish retains mercury from its diet over time. Top predators often have high concentrations due to both processes, but here the focus is on one organism's buildup, not chain-wide amplification. Choice B misapplies biomagnification to a single organism over time rather than across levels. Choice C incorrectly states mercury decreases at higher levels, and choice D wrongly claims mercury is rapidly excreted, preventing buildup.
DDT was sprayed near wetlands decades ago. Today, a heron that eats fish has 9 ppm DDT in its fat tissue, while the fish it eats average 2 ppm. Which term best describes why the heron’s concentration is higher than the fish’s?
Bioaccumulation, because the heron’s tissues prevent any chemical from being stored.
Biomagnification, because DDT is quickly metabolized and therefore concentrates in prey.
Biomagnification, because DDT concentration increases at higher trophic levels.
Bioaccumulation, because DDT increases as you move up trophic levels from prey to predator.
Explanation
Bioaccumulation is the process of toxins accumulating in an organism over time, while biomagnification is the increase in toxin concentration from one trophic level to the next. Here, the heron (9 ppm DDT) has more than its fish prey (2 ppm) due to biomagnification, as it consumes multiple fish, amplifying the persistent DDT. Top predators like herons have the highest levels because toxins are transferred and concentrated through the food chain without significant breakdown. Choice A swaps the terms; choice C errs by saying DDT is quickly metabolized; and choice D claims tissues prevent storage, which is false.
A lake received PCB runoff for several decades. Scientists measured average PCB concentrations (ppm) in organisms: phytoplankton 0.02 ppm, zooplankton 0.10 ppm, small fish 0.80 ppm, large predatory fish 4.0 ppm, and osprey eggs 12 ppm. Which statement best describes what is happening and why the osprey eggs have the highest concentration?
Biomagnification is occurring because PCBs are persistent and fat-soluble, so concentrations increase up the food chain to top predators like ospreys.
Biomagnification is occurring because PCBs break down quickly, causing higher concentrations only in organisms with shorter lifespans.
Bioaccumulation is occurring because PCB concentration increases at each higher trophic level, leading to the highest levels in top predators.
Bioaccumulation is occurring because ospreys absorb PCBs directly from the air, not from food.
Explanation
Bioaccumulation refers to the buildup of a toxin within a single organism over time as it absorbs more than it eliminates, often through direct exposure or diet. Biomagnification, on the other hand, is the process where toxin concentrations increase at successively higher trophic levels in a food chain because predators consume multiple prey items that have already accumulated the toxin. In this lake scenario, PCB concentrations rise from phytoplankton (0.02 ppm) to zooplankton (0.10 ppm), small fish (0.80 ppm), large fish (4.0 ppm), and osprey eggs (12 ppm), illustrating biomagnification as the toxin amplifies up the chain. Top predators like ospreys have the highest concentrations because they eat large quantities of contaminated prey, and since PCBs are persistent and fat-soluble, they are stored in tissues rather than excreted. Choice A incorrectly attributes the pattern solely to bioaccumulation without recognizing the trophic level increase. Choice C is wrong because ospreys primarily get PCBs from food, not air, and choice D errs by claiming PCBs break down quickly, which they do not.
In an estuary contaminated with DDT, measured concentrations were: water 0.000003 ppm, algae 0.04 ppm, shrimp 0.20 ppm, mullet 1.0 ppm, and pelicans 7.0 ppm. Which prediction best matches the process shown if a new apex predator (e.g., a dolphin) that eats mullet is introduced?
The dolphin would have the same DDT concentration as the water because DDT is not stored in tissues.
The dolphin would likely have a higher DDT concentration than mullet due to biomagnification up the food chain.
The dolphin would likely have a lower DDT concentration than mullet because toxins dilute at higher trophic levels.
The dolphin would have lower DDT because bioaccumulation occurs only in producers, not consumers.
Explanation
Bioaccumulation describes how toxins build up in an individual organism through continuous exposure, while biomagnification refers to the increasing concentration of toxins as they move up trophic levels via predation. In this estuary, DDT levels rise from water (0.000003 ppm) to algae (0.04 ppm), shrimp (0.20 ppm), mullet (1.0 ppm), and pelicans (7.0 ppm), demonstrating biomagnification. Introducing a dolphin that eats mullet would likely result in even higher DDT in the dolphin due to consuming multiple contaminated mullet, amplifying the toxin at the apex level. Top predators accumulate the highest levels because they ingest the cumulative toxins from many prey items lower in the chain. Choice B is incorrect as toxins concentrate, not dilute, up the chain; choice C errs by saying DDT is not stored; and choice D wrongly limits bioaccumulation to producers.
A food web contains phytoplankton → anchovies → tuna → shark. If mercury concentration in anchovies averages 0.05 ppm and tuna average 0.4 ppm, which is the most reasonable expected mercury concentration in sharks, assuming typical biomagnification and similar diets over time?
Much higher than 0.4 ppm, because mercury biomagnifies toward top trophic levels.
Approximately 0.05 ppm, because mercury returns to baseline at higher trophic levels.
Zero ppm, because mercury cannot enter marine food webs.
Lower than 0.05 ppm, because sharks excrete mercury faster than they ingest it.
Explanation
Bioaccumulation is the net buildup of a toxin in an organism over its lifetime, while biomagnification amplifies concentrations up the food chain as higher predators consume many lower ones. Given anchovies at 0.05 ppm and tuna at 0.4 ppm, sharks as top predators would likely exceed 0.4 ppm due to biomagnification of mercury through diet. Top predators have the highest levels because they integrate toxins from numerous prey, and mercury's persistence prevents easy elimination. Choice B wrongly suggests levels return to baseline; choice C claims faster excretion in sharks, which is false; and choice D denies mercury enters food webs, which it does.
PCBs are fat-soluble and resistant to breakdown. Which scenario best illustrates biomagnification rather than bioaccumulation?
PCB concentration in river water decreases after a cleanup project.
PCB concentration is higher in eagles than in the fish they eat.
A single trout’s PCB level increases as it ages from 1 year to 5 years.
A mussel filters water and removes PCBs, lowering its tissue concentration over time.
Explanation
Bioaccumulation is toxin buildup in one organism over time, while biomagnification is the amplification across trophic levels. The scenario of higher PCBs in eagles than fish illustrates biomagnification, as eagles consume many fish, concentrating the persistent, fat-soluble PCBs. Top predators have highest levels due to this trophic transfer. Choice A shows bioaccumulation in one trout; choice C depicts environmental change, not either process; and choice D shows toxin removal, opposite of accumulation.
In a coastal marsh, DDT in sediment remains detectable decades after use. Snails feeding on detritus show increasing DDT levels the longer they live, even if they do not change their diet. Which term best describes this pattern in snails?
Biomagnification, because snails are higher trophic level predators.
Bioaccumulation, because DDT is water-soluble and rapidly excreted.
Biomagnification, because DDT becomes less concentrated at higher trophic levels.
Bioaccumulation, because DDT persists and builds up within an organism over time.
Explanation
Bioaccumulation describes toxin increase within an organism over its lifespan, whereas biomagnification is across trophic levels. Snails show rising DDT with age despite consistent diet, exemplifying bioaccumulation from persistent sediment exposure. In ecosystems, top predators have high levels via biomagnification. Choice A misapplies to trophic position; choice C states opposite of concentration increase; and choice D errs on solubility and excretion.
A river has a low but constant methylmercury concentration. Over several months, the mercury level inside mayfly larvae steadily increases even though the larvae remain at the same trophic level and eat the same type of algae. What process is this?
Bioaccumulation, because mercury builds up within an organism over time.
Biomagnification, because the mayflies are predators.
Bioaccumulation, because mercury cannot enter organisms through food.
Biomagnification, because mercury concentration is always highest in producers.
Explanation
Bioaccumulation refers to the increasing concentration of a toxin in an individual organism over time due to ongoing exposure. Biomagnification describes toxin amplification across trophic levels. The mayfly larvae show steadily increasing mercury despite stable diet and trophic level, illustrating bioaccumulation from continuous intake exceeding elimination. In broader contexts, top predators have high concentrations via biomagnification, but this focuses on time within one level. Choice A misapplies biomagnification to non-predators; choice C wrongly states highest in producers; and choice D denies food-based entry, which occurs.
A biologist explains: “Even if the concentration of PCBs in the water is extremely low, top predators can still end up with dangerous levels.” Which mechanism best supports this claim?
PCBs are highly volatile, so they evaporate and concentrate only in the atmosphere.
PCBs are broken down into more concentrated forms only in producers, not consumers.
PCBs are nutrients, so predators intentionally store them for energy.
PCBs are persistent and lipophilic, so they bioaccumulate in organisms and biomagnify at higher trophic levels.
Explanation
Bioaccumulation involves toxin buildup within one organism, whereas biomagnification leads to higher concentrations at upper trophic levels. The biologist's claim is supported by PCBs being persistent and lipophilic, allowing them to bioaccumulate in individuals and biomagnify up the chain to dangerous levels in top predators, even from low water concentrations. Top predators amass high levels by consuming many contaminated prey, storing the fat-soluble PCBs. Choice B is incorrect as PCBs do not primarily concentrate in air; choice C mislabels them as nutrients; and choice D wrongly attributes concentration to producers only.
A pesticide containing DDT enters a marsh. Over several months, a single heron continues eating contaminated fish. Measurements show the DDT concentration in the heron’s fat tissue rises from $2\ ppm$ to $9\ ppm$ even though the average DDT concentration in its fish prey stays about $1\ ppm$ during that time. Which choice best describes the process shown and the most likely reason the concentration increases?
Bioaccumulation; DDT concentration increases within the heron over time because it is persistent and lipophilic, so intake exceeds elimination.
Bioaccumulation; DDT concentration increases mainly because the heron is moving up trophic levels during the season.
Biomagnification; DDT concentration increases because the water concentration must be increasing even if fish concentrations are constant.
Biomagnification; DDT concentration increases within one organism because it is stored in fat and is not readily metabolized or excreted.
Explanation
Bioaccumulation is the gradual buildup of a toxin within an individual organism over its lifetime, typically from repeated exposure through diet or environment, where intake exceeds the rate of metabolism or excretion. Biomagnification differs by describing the amplification of toxin concentrations across successive trophic levels in a food chain, as predators ingest contaminated prey. In this case, the heron's DDT concentration in fat tissue increases from 2 ppm to 9 ppm over months while feeding on fish with a stable 1 ppm, illustrating bioaccumulation because the persistent, lipophilic nature of DDT causes it to accumulate in the heron's body faster than it is eliminated. Top predators often have the highest concentrations in biomagnification scenarios due to consuming many lower-level organisms, but here the focus is on temporal buildup within one organism, not across levels. Choice A wrongly labels it biomagnification while describing bioaccumulation mechanics. Choice C incorrectly assumes rising water concentrations drive biomagnification, despite constant fish levels, and choice D misapplies bioaccumulation to trophic level shifts that aren't occurring. Therefore, choice B correctly identifies bioaccumulation and explains the intake-elimination imbalance.