In environmental science, which of the following is considered the largest single source of pollution in the world by volume?

Introduction / Context:
Pollution comes from many sources, including agriculture, transport, industry, and households. This question aims to check your understanding of which type of pollution source contributes the largest volume of waste globally and affects water bodies, soil, and urban environments. Instead of focusing only on toxicity, the question emphasises the largest source in terms of sheer quantity and widespread impact.

Given Data / Assumptions:

• The options include agricultural chemicals, automobile exhausts, sewage and garbage, and industrial effluents.
• The phrase largest source of pollution refers primarily to volume and widespread distribution, not just toxicity per kilogram.
• We consider global or broad national patterns, not a single city or region.

Concept / Approach:
Everyday human activities produce vast amounts of waste. While herbicides and insecticides are dangerous pollutants, their mass is far smaller than the total volume of domestic sewage and urban solid waste produced daily. Automobile exhausts are a major source of air pollution in cities, contributing to smog and greenhouse gas emissions, but again they represent primarily gaseous emissions rather than the enormous volume of mixed wastes. Industrial effluents can be extremely toxic and locally significant, yet the total quantity of household sewage and municipal garbage discharged into rivers, lakes, oceans, and landfills is generally much larger. Domestic sewage includes wastewater from toilets, kitchens, and bathrooms; solid garbage includes food waste, plastics, paper, and other household refuse. These wastes are produced by almost every person every day, making sewage and garbage the largest single source of pollution when considered globally.

Step-by-Step Solution:

Verification / Alternative check:
Environmental studies literature often highlights municipal solid waste and domestic sewage as major challenges for developing and developed countries alike. Urban local bodies spend significant portions of their budgets on waste collection and sewage management. Reports on river pollution in countries like India often attribute high levels of organic and bacterial contamination primarily to untreated domestic sewage, with industrial effluents contributing additional but smaller portions by volume. Global analyses of marine litter show that a significant fraction of plastics and debris originate from mismanaged municipal solid waste, not just industrial sources. This evidence supports the conclusion that sewage and garbage form the largest single source of pollution.

Why Other Options Are Wrong:

Herbicides and insecticides used in agriculture are wrong as the largest source by volume because they are applied in smaller quantities, even though they are highly toxic and persistent pollutants.

Automobile exhaust emissions from vehicles are incorrect because they mainly contribute to air pollution and greenhouse gas emissions, not the bulk of solid and liquid waste pollution by mass.

Industrial effluents discharged from factories are also wrong here because, while dangerous and concentrated, they do not match the total global volume of domestic sewage and municipal solid waste generated every day.

Common Pitfalls:
Students may focus only on how dangerous a pollutant is and overlook how much of it is produced. This leads them to choose options like industrial effluents or pesticides because they sound more harmful. To answer correctly, it is important to distinguish between toxicity and volume. In this question, the focus is on the largest source in terms of total waste produced. Therefore, sewage and solid garbage generated by households and cities are considered the largest single source of pollution in many environmental contexts.

Final Answer:
Thus, the largest source of pollution in the world by volume is sewage and solid garbage generated by households and cities.