Sewage contains a host of toxic chemicals that can kill fish and threaten human health. Most people think that all sewage is fully treated at a sewage treatment plant and enters the ocean relatively clean. Some wastewater engineers portray sewage as being largely human waste that is dispersed well in tidal currents with no effect on the environment. Think again.
What’s in Sewage?
In fact, sewage contains hundreds of toxic chemicals dumped into the sewage system by households, businesses and industries. Some are harmful in very low concentrations. Some toxins combine with others in this deadly brew to create new compounds that are even more dangerous.
Some heavy metals and persistent chemicals that stay in the body biomagnify as they work their way up the food chain.
Effects on Fish & Other Marine Life
The organic waste in sewage is not benign. Dissolved oxygen in ocean water is used up by bacteria that feeds on decomposing organic material. This oxygen demand can literally suffocate fish and other sea creatures. Sewage also contains large amounts of suspended particles of matter that can prevent sunlight from reaching underwater plants that are the food source for so many species. Suspended solids can also cause abrasions on the gills of fish or delicate membranes of other organisms.
Slow Death For Marine Life
Even small amounts of the most hazardous chemicals found in sewage can cause irreparable harm to fish, particularly juveniles. The result is not immediate and visible like the aftermath of an oil spill. There are no fish floating dead on the surface. It is a quiet, unseen death over time. Dead and dying fish are simply eaten by other marine organisms.
Death comes in a variety of ways. Some chemicals suppress the immune system allowing the onset of disease. Heavy metals, pesticides, persistent organochlorines, plastics, surfactants and aromatic hydrocarbons can disrupt the endocrine system interfering with sexual and bone development.
The toxins found in sewage can also change fish behaviour, inhibiting normal swimming, schooling and migration in ways that significantly reduce their chances for survival.
Bioaccumulation
Some heavy metals and persistent chemicals that stay in the body biomagnify as they work their way up the food chain. Larger fish eating large numbers of contaminated smaller fish can end up with thousands or millions of times the level of toxins than the organisms that first absorbed them.
Stormdrains Add Toxic Load
Stormwater is laced with sediment, grease and toxins from cars, trucks and illegal dumping. Many people think that the stormdrains they see on most streets just carry off small amounts of harmless rain. In fact, discharges from stormwater outfalls are roughly the same volume as sewage and contain many of the same dangerous toxins found in sewage.
Stormdrain Runoff Harmful to Fish
Although the concentrations of toxins are not as acute as those in the sewage, the first hour of runoff after a heavy rain can contain seriously harmful levels of oil, grease, nitrogen, phosphorus, hydrocarbons, metals and suspended solids.
Oil, antifreeze and other compounds leak from cars and trucks, staining parking stalls in every parking lot. All this eventually runs into the stormdrain system. Car and truck exhausts emit PAHs and other toxins that settle on our roadways only to wash into the storm sewer during the next rain. These chemicals are linked to liver lesions and cancer in fish and are known to biomagnify through the food chain.
Leftover hazardous wastes are inadvertently or purposely dumped down stormdrains. Car washing detergents and pesticides in gardens and lawns often end up in the system.
Source: Victoria Sewage Alliance
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written by Guillermo , March 03, 2010