Question

18 the fish in a stream running by a small town are dying in large numbers. why might chemical hazards be suspected?
biomagnification
19 think visually in each arrow, write one way that a chemical such as ddt can get into waterways. in each block, add dots to represent levels of chemical concentrations and how they change due to biomagnification.
image of a biomagnification pyramid with water, producers, zooplankton, small fish, large fish, fish - eating birds and two arrows pointing to water
20 how did high concentrations of ddt affect bird populations?
21 explain why a persistent organic pollutant (pop) is a problem that is often handled by international agreements or treaties.

Explanation:

Question 18

Chemical hazards are suspected because chemicals from human activities (like industrial waste, agricultural runoff with pesticides/fertilizers, sewage) can contaminate the stream. These chemicals can be toxic to fish, disrupting their physiology (e.g., gill function, reproduction) or causing bioaccumulation/biomagnification, leading to mass deaths.

Arrows (Ways to Introduce DDT to Waterways):

• Left Arrow (e.g., Agricultural Runoff): Rain washes DDT from farm fields (where it’s used as a pesticide) into the stream.
• Right Arrow (e.g., Industrial Discharge): Factories release wastewater containing DDT or DDT - contaminated byproducts into the waterway.

Blocks (Chemical Concentrations via Biomagnification):

• Water: Few dots (low concentration, as DDT dissolves or is absorbed by producers).
• Producers (e.g., Algae): Slightly more dots (absorb DDT from water; bioaccumulation starts).
• Zooplankton: More dots (eat producers, accumulating DDT).
• Small Fish: Even more dots (eat zooplankton, DDT concentrates further).
• Large Fish: Many dots (eat small fish, higher DDT levels).
• Fish - Eating Birds: Most dots (top predator, highest DDT concentration due to biomagnification).

High DDT concentrations in birds (from biomagnification, as they eat DDT - laden fish) cause eggshell thinning. Thin eggshells break easily during incubation, reducing successful hatching. Also, DDT disrupts the birds’ endocrine system, affecting reproduction and behavior, leading to population declines (e.g., bald eagles were severely impacted).

Answer:

Chemical hazards are suspected as human activities (industrial waste, agricultural runoff, sewage) can introduce toxic chemicals into the stream, harming fish via toxicity, bioaccumulation, or biomagnification.

Question 19