Amazon Soil Contamination Characterization

What is Soil Contamination?

Soil contamination is the mixing of hazardous substances with the soil. These contaminants get physically or chemically attached to the soils or are trapped within its particles

What types of soil contamination are present in the Amazon and where?

The main types of soil contamination in the Amazon Basin Rainforest are :

Mercury contamination – This is found in the areas along the Tapajos River where gold mining is carried out by an estimated million miners. Mercury is used for the extraction of gold from river sediments. Though most of this contamination is found in the river water, some of it eventually gets to the land in the form of silted soil deposited on river plains when there’s flooding.

Mercury contamination is also resulting from the exposure of naturally occurring deposits where a lot of vegetation is lost during deforestation

Cyanide contamination. Continuous loss of vegetation speeds up the erosion process and this eventually gets to Mercury layers.

Cyanide Contamination

The main source of cyanide contamination is gold mining operations. A notable site of this pollution is the Omai gold mines in Guyana to the north of Brazil.

Pesticide contamination

This is most prevalent in areas where agriculture is being carried out. Although pesticides are mostly used in crop cultivation which is not as significant as cattle ranching, as far as Amazon depletion is concerned, their effect is felt in areas that are newly cleared for cultivation. The immigrants from the cities are ill equipped with not only agricultural but environmental conservation skills and so use chemicals of various kinds recklessly.

How do these affect the health of the Amazon Soil and Land?

Soil contamination mostly makes it impossible for healthy vegetation to grow on the affected land. When the plants absorb these contaminants through their roots they either develop weak stems, deformed leaves or reproductive failures. Some of the contaminants also slow the growth and development of the vegetation making recovery in areas where the forest has been cleared ineffective.

Animals in the rain forest are also not spared these adverse effects. Burrowing animals come into direct contact with the mercury in the soil. This has been found to interfere with respiratory processes and even brain damage. This leads to immature deaths of these animals. Animals are part of the Amazon ecosystem and this contamination is affecting them adversely.

Some of the soil contaminants are carried in the air where there is wind erosion and these are inhaled by the fauna in various quantities. This is especially the case with mercury and cyanide. Animals also absorb contaminants when they feed on contaminated vegetation.

How can the soil contamination be minimized or stopped?

Contamination resulting from mining can be reduced by the adoption of more environmental friendly mining techniques. A good method to be considered is the HGP technique that is being used by a US company, Orex. The proponents of HGP- Haber Gold Process claim that it extracts gold in bulk in significantly less time than is possible with cyanide. It also uses fewer reagents than cyanide meaning that it should be significantly cheaper. Most importantly however, it has no adverse effects environment.

Containment of contaminated soil. This can be done where cyanide is used for the gold extraction. A tailings dam can be constructed where hazardous material is settled to degrade naturally.

Recycling. This is done to the water in the mining operations. The water from the tailings dam can be used in the gold extraction processes. This reduces the amount of fresh water that becomes contaminated by mine wastes.

Phytoremediation. This is growing contaminant absorbing plants. It has been observed that some plants absorb Mercury. A typical example is the Arabidopsis, a mustard plant and other species that have been developed scientifically. The same technique may thus be used to remove other contaminants such as pesticides and herbicides.

Chemical and water flushing. This is employed in areas of little contamination where the affected soil is treated by chemical or water flushing.

Strategy for monitoring the Soil contamination

Several techniques have been developed to monitor the levels of contaminants in the soil. One of these methods is to measure the amount of mercury emissions using isolation flux chambers. This method is good because it samples over an area much larger than a typical soil sample. Information on this mercury measurement technique has been obtainmed from an article titled"Measurement of Mercury Flux from Treated Soil" by the Energy and Environmental Rsearch Centre of the University of North Dakota. 

Flux measurements are also safe because they do not require any handling of the soil which can be unsafe where there are high levels of contamination.

The active chamber is also good because it provides both real-time and diurnal variations in emission rates.

The active flux chamber consists of a stainless steel cylinder covered with a Plexiglas dome. Air is delivered from the breathing zone into the flux chamber with a low-flow pump so that a circulating flow pattern is obtained in the dome. The air inflow is set so that the inside temperature approximates the ambient soil temperature. A pressure relief port prevents the interior pressure from exceeding ambient conditions while the atmosphere in the flux chamber equilibrates. Upon equilibration, air temperature and mercury vapor concentration are measured in the center of the dome. The mercury flux is then calculated from the pump flow rate, the net concentration in the flux chamber, and the surface area enclosed by the chamber.

Hopefully, similar techniques can be identified to monitor other contaminants.