The Toxic Dangers of Flash Floods

By Mohamad Pauzi Zakaria

IN recent weeks, Kuala Lumpur has experienced severe flash floods. Traders along the Gombak and Klang rivers and other areas in the city lost goods and their property was damaged.

Large volumes of water flowed into every nook and corner of the city, carrying garbage, suspended sediment, liquid waste, dead animals and so on. Toxic material was among the waste which was swept away.

* Hydrocarbons

Petroleum hydrocarbon pollution in Malaysian towns and cities has been a major concern over the past five years with a phenomenal increase in industrialisation, urbanisation and motorisation.

Among the most toxic substances known to man, petroleum hydrocarbons are generated from industrial processes and human activities.

These widespread contaminants cause serious environmental problems because of their toxic, mutagenic and carcinogenic properties, persistence and bio-accumulation. Some components of hydrocarbons can disrupt the human endocrine system.

Crankcase oil in the oil sump of poorly maintained automobiles often leaks onto city streets and is found in street dust.

Other sources of hydrocarbons in urban areas include dry and wet soot particles from industrial and combustion sources.

These particles are swept away by wind and settle on grass, bushy vegetation and even soil. The hydrocarbon-laden particles and street dust are quickly redistributed by runoff during floods.

Some particles may also be transported to estuaries and to the open ocean. Despite the potential for direct discharge of petroleum hydrocarbons from urban runoff during heavy rainfall and floods into rivers, very little is known of their potential environmental impacts.

In water, hydrocarbons generally settle on the surface of suspended sediments, solids and colloids to become larger particles that can easily be taken up by aquatic organisms such as fish and shellfish.

When humans consume these organisms, they face acute and chronic health risks.

* Heavy metals

Heavy metals such as chromium, lead, arsenic, mercury and cadmium are extremely toxic to man and animals. They can cause major damage to the central nervous system and disrupt our metabolic and enzymatic systems.

Perhaps the most infamous environmental disaster in recent memory was the mercury poisoning in Minamata Bay in Japan in the 1950s and 1960s.

Over 10,000 coastal residents ate shellfish contaminated with mercury. Some were killed and others suffered from numbness and blurred vision, while children born during those two decades had birth defects.

These metals are among the raw materials of consumer products. However, during industrial processes, especially in small and medium scale enterprises, these metal chips and powders spread across the floor and stick to the wall and ceiling of factories as dust.

During flash floods, the metal dust is easily washed away and redistributed elsewhere. The metals are ingested by organisms or settle as sediment which is released again during flash floods.

* Pharmaceuticals, drugs and hormones

Waste from the production of pharmaceuticals, drugs and hormones are one of the latest environmental concerns. In the more industrialised countries, these waste are constantly monitored and appropriate remedial measures to reduce such pollutants in the environment are among the top priorities.

During floods, pharmaceutical, drug and hormone waste can easily be redistributed and transported into water channels and rivers. Micro-organisms will uptake the waste and develop resistance to the antibiotics or it may change their immune systems. This poses far- reaching consequences for the health ecosystem.

* Drugs used in animal husbandry

Veterinary drugs or growth promoters (particularly in large- scale animal farming and intensive livestock treatment) and their metabolites are excreted with manure. Farmers use manure and sewage sludge to fertilise fields, introducing residues of the drug into the soil.

Veterinary pharmaceuticals may reach surface water as runoff from the soil after heavy rain. The wash-off from topical treatment may enter soil or ambient waters directly. Application of pharmaceuticals in aquaculture also results in direct input into water and sediments.

Experts are increasingly concerned about the growing resistance of pathogenic bacteria in the environment, and their eco-toxic effects. Increasingly, antibiotic resistance is seen as an ecological problem. This includes both the ecology of resistant genes and that of the resistant bacteria themselves.

* Detergents and surfactants

In urban areas, detergents used in homes are normally biodegradable and have little impact on the environment. However, industrial strength detergents used in machine cleansing, overhaul of engines and the car wash industry are more persistent in the environment.

Metals and toxic additives in the detergents are released in wastewater and contaminate surrounding sedimentary environments.

During floods, this detergent waste is also redistributed and transported elsewhere. The detergents can change the surface tension of water bodies which makes it difficult for aquatic organisms living near the water surface to come up for air or to feed.

* Sewage

Sewage contains many pathogenic bacteria and viruses. In urban environments, faecal materials come from humans, rodents, insects and wild animals and end up as dust, powder and sometimes dried cakes in soil and underneath tree canopies.

Flash floods carry these faecal materials which re-dissolve into the water. Pathogenic bacteria and viruses are released from the dried cakes and can cause outbreaks of diseases such as dysentery, cholera, meningitis, influenza and conjunctivitis.

* Leachates

Landfilling and depositing of solid waste in open dumps have been the most common methods for the disposal of municipal solid waste, with an estimated nine million kilogrammes of waste generated and collected per day in Kuala Lumpur in 2005.

While the volume of leachates generated in an exposed landfill in urban areas may not be widespread, illegal dumping of solid waste is rampant in urban areas.

Collectively, these illegal dump sites and landfills may generate a significant amount of leachates that contain a variety of toxic pollutants including hydrocarbons, metals, dioxins, insecticides, pharmaceuticals and hormones.

During floods, toxic materials are simply swept away and redistributed, causing severe environmental impacts and ecosystem damage.

With all these environmental impacts, flooding must be prevented or reduced to maintain the health of city dwellers and prevent them from being exposed to pollutants.

* The writer is an associate professor with the Faculty of Environmental Studies at Universiti Putra Malaysia. He can be contacted at mpauzi@env.upm.edu.my

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