Sewage Pollution Introduction

Sewage pipe. Photo © Joe Miller

Wastewater pollution is a growing threat to people and marine life and makes up the largest percentage of coastal pollution worldwide. ref Globally, an estimated 80 percent of wastewater is discharged into the environment untreated. ref Research shows that wastewater pollution often occurs in proximity to coral reefs around the world due to nonexistent or inadequate wastewater management. ref

Terminology: Sewage vs Wastewater

Sewage has come to mean any human excrement, regardless of where and how it has been stored or transported. Where plumbing and centralized sewer systems are in place, sewage discharges are often called wastewater, which includes household wastes like phosphates and a host of chemicals of emerging concern, as well as urban run-off and associated pollutants. Additionally, human waste includes endocrine disruptors, pharmaceuticals, recreational drugs, petrochemicals, pathogens, and more. All of these contaminants pose a threat to ocean and human health and are part of sewage pollution.

Major coastal cities and urban environments are usually significant sources of pollution, especially in low-income countries. However, even in high-income countries this challenge is present. For instance, more than 1.2 trillion gallons of effluent (including untreated wastewater, stormwater, and industrial waste) are discharged into waterways in the United States every year. ref There are approximately 4.5 billion people that do not have access to safe sanitation. Included in this group are 2.5 billion people that have no toilets at all and an estimated 1 million practice open defecation. ref

Map sewage pollution

Documented coastal wastewater pollution in 104 of 112 areas with coral reefs. Source: Wear and Vega Thurber 2015

Typical components of wastewater include freshwater, nutrients, organic matter, bacteria, viruses, parasites, endocrine disruptors, suspended solids, pharmaceuticals, micro and macro plastics, household chemicals, petrochemicals, sediments and heavy metals—each of which individually and together work to harm coastal and marine ecosystems. ref The high volume of wastewater humans discharge into the ocean degrades critical habitats, kills marine life, harms ecosystems upon which humans depend, and threatens human health.

The impacts of wastewater pollution vary and is influenced by population, geography, and infrastructure. Wastewater pollution can be linked to the following impacts ( opens in a new windowOur Shared Seas):

  • Physical and biological damage to coral reefs, seagrasses, and salt marshes where it can smother habitat, lead to high levels of local acidification, and increase risk of disease. ref
  • Eutrophication due to nutrient overload that depletes oxygen, kills marine flora and fauna, and disrupts ecological processes. ref
  • Loss of coastal ecosystem services, like erosion control, buffers from storms, and nurseries for juvenile fish. ref
  • Harmful algal blooms that can produce toxins or physical material (e.g., sargassum seaweed) that kill marine life, close beaches, and can cause human disease through direct exposure and indirectly through consumption of contaminated seafood. ref
  • Animal and human diseases resulting from pathogens, heavy metals, and toxic chemicals that can cause acute disease, as well as long-term disruptions to biological processes. ref
  • Contamination of fisheries and fish mortality as well as reductions in species diversity in polluted areas. These impacts are due to both direct effects of wastewater pollution on individual fish as well as decreased dissolved oxygen (due to increases in nutrient levels) and algal toxins. ref

When wastewater enters the ocean and mixes with seawater, pollutants are dispersed and diluted. This has led to a persistent assumption that “the solution to pollution is dilution”. However, ongoing wastewater contamination limits the ocean’s capacity to dilute those contaminates, particularly in areas with limited tidal flux, or vulnerable biodiversity. Strategies to collect and treat wastewater can effectively avoid further pollution of the ocean, although treated effluent can also be harmful due to contaminants left behind by outdated or inadequate treatment. See Impacts on Marine Life and Impacts on Human Health for additional information on the effects of wastewater pollution.

Climate change (specifically rising temperatures, sea levels, and ocean acidification) intensifies the impacts of wastewater pollution. Oxygen depletion, resulting from nutrient loading and corresponding algal blooms, leads to increased production of nitrous oxide, a greenhouse gas further contributing to climate change. As global populations and climate change threats increase, the need to mitigate wastewater pollution in the ocean is becoming more critical. Reef managers can engage in addressing this threat and help ensure that sanitation interventions consider natural ecosystems.

Watch the webinar on Addressing the Threat of Ocean Sewage Pollution:

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