Aquatic toxicity in environmental engineering Which constituents in a water stream are particularly harmful (deleterious) to aquatic life and therefore must be controlled in wastewater treatment?

Introduction / Context:
Protecting aquatic life is a central objective of environmental engineering. Different classes of pollutants stress fish and invertebrates in distinct ways. This question checks recognition of the main harmful groups commonly encountered in industrial and municipal effluents.

Given Data / Assumptions:

• A water stream may carry dissolved organics, suspended solids, and toxic inorganics.
• We are concerned with ecological effects on fish, macroinvertebrates, and overall aquatic health.
• No special receiving-water dilution is assumed; impacts are considered at typical concentrations of concern.

Concept / Approach:
Deleterious effects arise via toxicity, oxygen depletion, habitat alteration, and bioaccumulation. Soluble toxic organics can be acutely or chronically toxic. Suspended solids reduce light penetration, clog gills, smother eggs, and carry attached toxics. Heavy metals and cyanides are well-known acute toxins; metals can bioaccumulate and cause long-term sublethal effects.

Step-by-Step Solution:

Verification / Alternative check:
Regulatory frameworks (e.g., limits on BOD, TSS, metals, and CN) reflect these risks. Biological monitoring (fish kills, macroinvertebrate indices) correlates spikes in any of these pollutants with ecological damage.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming only “toxicity” matters; in reality, non-toxic solids still damage aquatic habitats. Also, some pollutants bind to solids, compounding effects.

Final Answer:
all (a), (b) & (c).