Category: Physical hazards

The quantity and distribution of fresh water pose one set of environmental and social challenge. Safeguarding the quality of water involves another collection of environmental and human health dilemmas. Developed nations have made admirable advances in clearing up water pollution over the past few decades. Still, the World Commission on Water recently concluded that over half the world’s major rivers are “seriously depleted and polluted, degrading and poisoning the surrounding ecosystems, threatening the health and livelihood of people who depend on them”.

The term pollution describes the release of matter or energy into the environment that causes undesirable impact on the health and well-being of people or other organisms. Pollution can affect water, air or soil, and can be:

  • Physical  – scientists use temperature, color and turbidity, which measures the density of suspended particles in a water sample. Fast-moving rivers that cut through arid or eroded landscapes, such as the Colorado River, carry a great deal of sediment and are turbid and muddy-looking as a result. If scientists can measure only one parameter, they will often choose turbidity, because it tends to correlate with many others and is thus a good indicator of overall water quality.
  • Chemical –nutrients concentrations, pH, taste and odor, and hardness. Hard water contains high concentrations of calcium and magnesium ions, prevents soap from lathering, and leaves chalky deposits behind when heated or boiled. An important characteristic is dissolved oxygen content, which is an indicator of aquatic ecosystem health because surface waters that are low in dissolved oxygen support less aquatic life.
  • Biological – is the presence of fecal coliform bacteria, which indicates contamination by human waste and suggest the presence of other disease-causing organisms. Scientists can identified biological pollution using algae and aquatic invertebrates.


Water pollution comes in many forms and can cause diverse impacts on aquatic ecosystems and human health:

  • Pathogens and waterborne diseases – disease-causing organisms (pathogenic viruses, protists, and bacteria) can enter drinking water supplies when these are contaminated with human waste or with animal waste from feedlots. Biological pollution by pathogens causes more human health problems than any other type of water pollution. Treating sewage constitutes one approach for reducing health risks. Another is using chemical or other means to disinfect drinking water. Personal hygiene is vital, as is government enforcement of regulations to ensure the cleanliness of food production, processing, and distribution.
  • Toxic chemicals – our waterways have become polluted with toxic organic substances of our own making, including pesticides, petroleum products, and other synthetic chemicals. Many of these can poison animal and plants, alter aquatic ecosystems, and cause an array of human health problems, including cancer. Toxic metals such as arsenic, lead, and mercury, as well as acids from acid precipitation and from acid drainage from mining sites, also cause negative impacts on human health and the environment. Legislation and enforcing stricter regulations of industry can help reduce releases of toxic chemicals. We can also modify our industrial process and our purchasing decisions to rely less on these substances.
  • Sediment – floods build fertile farmland, but sediment that rivers transport can also impair aquatic ecosystems. Mining, clear cutting, overgrazing, land clearing for housing development, and tilling of farm fields all expose soil to wind and water erosion. Some water bodies, such as the Colorado River and China’s Yellow River, are naturally sediment-rich, but many others are not. When a clear-water river receives a heavy influx of eroded sediment, aquatic habitat can change dramatically, and fish adapted to clear-water environments may not be able to adjust. We can reduce sediment pollution by better managing farms and forests and by avoiding large-scale disturbance of vegetation.
  • Thermal pollution – water’s ability to hold dissolved oxygen decreases as temperature rises, so some aquatic organisms may die when human activities heat water. When we withdraw water from a river and use it to cool an industrial facility, we transfer heat energy from the facility back into the river where the water is returned. The temperature might also be raised by removing streamside vegetation that shades water. Too little heat can also cause problems.  On the Colorado and other dammed rivers, water at the bottoms of reservoirs is colder than water at the surface. When dam operators release water from the depths of a reservoir, downstream water temperatures drop suddenly. In the Colorado’s system, these low water temperatures have favored cold-loving invasive trout over and endangered native species of suckerfish.


Among many aspects, environmental health is the examination of the impacts of human-made chemicals on wildlife and people. It’s study and practice allows us to understand the environmental factors that influence human health and quality of life. People who work with it seek to prevent adverse effects on human health and ecological systems.

There are many different types of environmental health threat, or hazard, around us. Some of those are risks that we cannot avoid, however, there is also some amount of risk that can be avoided by taking precautions. Environmental health consists of taking steps to minimize the impacts of hazards and the risks of encoutering them. Here I’m going to talk a little bit about some of them, but focuse more on the chemical ones.

Physical hazards – are the natural hazard previously mentioned on the last post. Therefore, they are processes that occur naturally like earthquakes, volcanic eruptions, fires, floods, blizzards, landslides, hurricanes, and droughts, but they also include ongoing natural phenomena, like ultraviolet (UV) radiation from sunlight, which can cause skin cancer, cataracts, and immune suppression in case of excessive exposure.

Practices like increase our vulnerability to some physical hazards:

  • Deforesting slopes makes landslides more likely;
  • Channelizing rivers makes flooding more likely in some areas while preventing flooding in others. For more information about this, click here.

The risk over these practices can be reduced by improving our forestry and flood control practices; by choosing not to build in areas prone to floods, landslides, fires, and coastal waves. For hazards like exposure to UV light, the risk can be reduced by using clothing and sunscreen to shield our skin from intense sunlight.

Biological hazards – result from ecological interaction among organisms. They consist on bacterial or virus infection or other pathogeny. This is infectious disease, and they are also called communicable or transmissible disease. Infectious diseases like malaria, cholera, tuberculosis, and influenza are considered environmental health hazards. Like the other two types of hazards, it’s impossible to avoid risks from biological agents, however, steps can be taken to reduce the likelihood of infection.

Cultural or lifestyle hazards– result from the place we live, our socioeconomic status, occupation, or behavioral choices. Choosing to smoke cigarettes or living or working with people who do, increases our risk of lung cancer. Choosing to smoke is a personal behavioral decision, but exposure to secondhand smoke may not be under one’s control. The same thing can be said for drug use, diet and nutrition, crime and mode of transportation. Advocates of environmental justice argue that such health factors as living in proximity to toxic waste sites or working unprotected with pesticides might be correlated with socioeconomic deprivation.

Chemical hazards – include the many synthetic chemicals produced by our society like disinfectants, pesticides and the compounds that contribute to reproductive problems on animals. Chemicals produced naturally by organisms can also be hazardous.

Despite diseases like cancer, heart disease, and respiratory disorders have genetic bases, they are also influenced by environmental factors. Asthma, for instance, is influenced by genes, but also by environmental conditions. As a matter of fact, pollutants from fossil fuels combustion makes it worse. Children raised on farms suffer less asthma than those raised in cities.

Malnutrition can foster many different illnesses, just like poverty and poor hygiene. Lifestyle choices can affect risks of acquiring som noninfectious diseases, just like smoking can lead to lung cancer and lack of exercise, to heart disease. Infectious diseases are responsible for 26%, nearly 15 milion deaths, that occur worldwide per year. Some pathogenic microbes attack us directly, whereas other times infection occurs through a vector, which is an organism that transfers the pathogen to the host. When it comes to infectious diseases there is a gap between the number of deaths in developed nations and the developing countries; differences in hygiene conditions and access to medicine makes infectious diseases be responsible for almost half of all deaths in developings, while there are very few deaths in developed nations.

Even though public health efforts have lessened the impact of infectious disease in developed nations, some cases like the West Nile Virus, acquired immunodeficiency syndrome (AIDS), avian flu and influenza. Other diseases like tuberculosis and malaria are evolving resistance to antibiotics. There are also some tropical diseases like malaria, dengue, cholera and yellow fever that might expand into the temperade zone with global climate change. Also, habitat alteration can affect the abundance, distribution, and movement of certain disease vectors.

There are some cases in which chemicals are used to fight diseases, even though they’re also hazardous to our health. This happens in Africa, where the pesticide DDT is used to kill the mosquitos that transmit malaria, because they’re considered to be a health threat greater than DDT.


It was only on the 60s that people began to learn about the risks of exposure to pesticides. The publication of Rachel Carson’s 1962 book, Silent Spring, was the key event that brought the pesticide dichlorodiphenyl-tricholoroethane (DDT) to public’s attention.

Synthetic Chemical

Synthetic chemicals are widely present in our environment, in fact, many of them have found their way into soil, air and water. A 2002 study by the US Geological Survey found that 80% of the US streams contain at least trace amounts of 82 wastewater contaminants, including antibiotics, detergents, drugs, steroids, plasticizers, disinfectants, solvents and perfumes, among other substances. The pesticides used to kill insects and weeds on farms, lawns, and golf courses are some of our most widespread synthetic chemicals. Because of this huge exposure, we carry traces of numerous industrial chemicals in our bodies.

Since not all synthetic chemicals pose health risks, and few are known as toxicants, we shouldn’t necessarily be alarmed. However, among the roughly 100,000 synthetic chemicals on the market today, few have been tested for harmful effects; therefore, we just do not know what are the effects, if any, so much different chemicals might cause to our organism.


Toxicants are not evenly distributed in the environment, and they move about in specific ways. Water, for example, carries toxicants from large areas of land and concentrates them in small volumes of surface water. Those chemicals that can persist in soil can leach down into groundwater and contaminate drinking water supplies. Many chemicals are soluble in water and enter organism’s tissues through drinking or absorption. That’s the main reason why aquatic animals like fish, frogs and stream invertebrates are effective indicators of pollution. Whenever scientists find low concentrations of pesticides exerting harm on frogs, fish, and invertebrates, they view this as a warning that people could be next. Toxicants might cause reproductive problems on animals and humans

The contaminants that wash into streams and rivers flow and seep into the water we drink and drift through the air we breathe.

The substances that can be transported by air makes the toxicological effect occur far from the site of direct chemical use. Airbone transport of pesticides is also called pesticide drift. This problem can be seen in the Central Valley of California, where irrigation, fertilizers and pesticides are used intensively. Dust particles containing pesticide residue and are transported by the wind for long distance and affected four species of frog in the mountains of Sierra Nevada.

Toxic agents may degrade quickly and become harmless, or may remain unaltered and persist for months, years or decades. The rate at the chemicals degradation depends on factors like temperatura, moisture and sun exposure, and how these factors interact with the chemistry of the toxicant. Those toxicans that persist in the environment have the greatest potential to harm organisms over long periods of time. In fact people are concerned about DDT and PCBs because of their long persistence time. 

There are natural toxicants that are also unhealthy and may cause us harm. However, scientists are still debating how much risk natural toxicants pose.