Environmental Chemistry Quiz 2

Aquatic invertebrates are used as biological indicators because they are sensitive to changes in water quality. Stonefly nymphs are particularly good indicators because they are very sensitive to pollution and can only survive in clean, well-oxygenated water. Therefore, the presence of stonefly nymphs indicates that the water is of high quality.

The LD50 value represents the lethal dose at which 50% of the test population dies. In this case, the statement indicates that when rabbits were injected with 34mg of arsenic per kilogram of body weight, 50% of them died. Therefore, the correct explanation is that 50% of the rabbit test population died when given 34mg/kg of body weight of arsenic.

This type of chemical indicator is used to determine the level of plant nutrients in a sample of water, indicating the presence of nitrogen and potassium. Nitrogen and potassium are essential nutrients for plants and are often found in fertilizers. By detecting the presence of these elements in water, the indicator can provide information about the nutrient levels available for plant growth.

The Mad Hatter is the correct answer because the passage states that headbands on hats were treated in mercury before the harmful effects of mercury were known. Since the Mad Hatter is known for wearing hats with a headband, it can be inferred that he may have been exposed to mercury, which could explain his abnormal behavior.

The correct answer is LD50 (Lethal Dose 50). LD50 refers to the amount of a particular chemical that is lethal and will cause death in 50% of the test population. This method is used to determine the harmfulness of a chemical by measuring the dosage that will result in a 50% mortality rate. It is commonly used in toxicology studies to assess the toxicity of substances and determine safe exposure levels.

The correct answer is "all at once" because if the specified dose is given to the subject group all at once, it is likely to cause a high level of toxicity or adverse effects, leading to a high mortality rate. This suggests that administering the dose all at once would result in the death of the entire subject group.

Chemical indicators are used to determine the level of plant nutrients in a sample of water. They are substances that change color or undergo a chemical reaction in the presence of specific plant nutrients, allowing for their detection and quantification. Unlike biological organisms or micro-biological organisms, chemical indicators do not rely on living organisms to indicate the nutrient levels. Instead, they provide a direct and objective measurement of the nutrient concentration in the water sample.

Accidental-exposure case studies provide valuable information about the chemical effects on humans. These studies involve individuals who have been unintentionally exposed to certain chemicals, allowing researchers to observe and analyze the resulting effects. Unlike experiments during the World Wars or stories that were once urban legends, accidental-exposure case studies are based on real-life scenarios and provide more reliable and concrete data. Therefore, they serve as a crucial source of information for understanding the effects of chemicals on human health.

Acid shock, caused by spring snow melt and runoff into streams and rivers, can have serious harmful effects on eggs and young offspring. The acidity of the water can negatively impact the development and survival of these vulnerable stages of organisms, potentially leading to population declines or even extinction. This is particularly relevant for species such as fish, amphibians, and aquatic invertebrates that rely on healthy water conditions for successful reproduction and early life stages.

Midge larvae are commonly found in water with low levels of dissolved oxygen. They have adapted to survive in such conditions and are able to extract enough oxygen from the water to sustain themselves. Stonefly nymphs, water boatmen, and mosquito larvae, on the other hand, require higher levels of dissolved oxygen and would be less likely to be found in water with a dissolved oxygen level of 2.

PCBs are known to be persistent organic pollutants that can bioaccumulate in the environment. This means that they can accumulate in the tissues of organisms and increase in concentration as they move up the food chain. As smaller organisms are consumed by larger ones, the PCBs are transferred and become more concentrated in the bodies of the top predators. Therefore, the level of PCBs is constantly monitored in parts per trillion to assess the potential risk to organisms at higher trophic levels.

Mosquito larvae are considered biological indicators because their presence in water bodies indicates poor water quality. Mosquitoes typically lay their eggs in stagnant or polluted water, making their larvae more likely to be found in such conditions. Therefore, the presence of mosquito larvae suggests the water may be contaminated or lacking in oxygen, making them a useful indicator species for assessing water quality.

Fresh spring water can have problems with water quality due to harmful acid content. The indicator of water quality referred to in the question is clarity. Clarity refers to how clear or transparent the water appears. If the water is cloudy or has impurities, it indicates poor water quality. Therefore, clarity is an important factor in determining the overall quality of fresh spring water.

This technology refers to a scrubber. A scrubber is a device used to remove pollutants from smokestack emissions. In this case, it is used to recover calcium sulfate (gypsum) from the emissions by reacting sulfur dioxide with calcium carbonate. The scrubber acts as a cleaning mechanism, trapping and removing the calcium sulfate particles from the smokestack emissions.

Water boatman is the correct answer because aquatic invertebrates are known as biological indicators as they can provide information about the quality of water. Water boatman, also known as Corixidae, are commonly found in freshwater environments and are sensitive to changes in water quality. They are often used as indicators of pollution or contamination in aquatic ecosystems. Their presence or absence, as well as their abundance, can provide valuable insights into the health of the water body.

Placing large boulders downstream would not increase the level of dissolved oxygen in the creek. Dissolved oxygen levels are typically increased by adding oxygen to the water or increasing the surface area for oxygen exchange. Adding ice to the water can increase dissolved oxygen levels by cooling the water and increasing its ability to hold oxygen. Planting additional water plants can increase dissolved oxygen levels through photosynthesis, where plants release oxygen into the water. Placing large boulders upstream can increase dissolved oxygen levels by creating turbulence and increasing the surface area for oxygen exchange. Therefore, placing large boulders downstream is the only option that would not contribute to increasing dissolved oxygen levels.

The LD50 of DDT is a measure of the lethal dose at which 50% of the test population will die. In this case, the LD50 is 87mg/kg for rats by mouth. This means that if rats are given 87mg of DDT for every kilogram of their body weight, 50% of them will survive.