Heavy Metal Soil Contamination Analysis by

Kenneth Rosales 5/20/10

ENVS 100W Winters

Heavy metal contamination in soil occurs in all parts of the world, but most often in

developing, undeveloped, and underdeveloped countries. Many measures have been taken to find

solutions, but unfortunately, it requires a great amount of time and effort to gain results.

Heavy metals may be carcinogenic, non-cancerous, cancerous and toxic, harmless, or

essential for life on earth. Non-cancerous consequences are due to toxins that can either have

neurological effects, immune effects, and/or endocrine effects (Lim and Schoenung 2010). Some

heavy metals include: Antimony (Sb), Arsenic (As), Barium (Ba), Beryllium (Be), Cadmium

(Cd), Chromium (Cr), Cobalt (Co), Copper (Cu), Lead (Pb), Mercury (Hg) Molybdenum (Mo),

Nickel (Ni), Selenium (Se), Silver (Ag), Vanadium (V), and Zinc (Zn) (Lim and Schoenung

2010). Heavy metal contamination usually occurs due to mines, landfills, Waste-to-Energy

facilities, or smelters (Bech et al., 1997; DMG, Liao, Probst, and Probst, 2005; 1995; King and

McCarthy, 2009). Heavy metals are extracted and refined resources that are used in everyday

products people use such as cell phones, speakers, or computers (EPA, 2010). Such activities of

generating heavy metal contamination to make merchandises in turn become social issues like in

the case of lead smelters adversely affecting low income residents in Boolaroo, Australia or

Northern Peru’s copper mining ordeal of farmland contamination (King and McCarthy, 2009;

Bech et al., 1997). Fortunately, there have been scientific advances in cleaning up heavy metals,

but much more research is needed for its success rate to increase substantially (Evangelou, Ebel,

and Schaeffer 2007). The issues of heavy metal pollutants will not only adversely affect

localities, but all life on a global scale if left alone. Therefore, the full adverse impacts can only

fully be understood and solved with economic, political, sociological, and scientific approaches.

Lead is an extremely toxic heavy metal utilized in many electronic products such as cell

phones, car batteries, computers, and solar panels (Lim and Schoenung, 2010; EPA, 2010; King

and McCarthy, 2009; Olszewski, 2010). Cell phones, car batteries, and computers are products

simultaneously soaring in global demand whereas solar panels are on the rise as humans struggle

to find solutions to energy and global warming issues. As the need for lead-based goods

increases, so do the social dilemmas residents face in Boolaroo, Australia.

Lead contamination in Boolaroo, Australia quantitatively and qualitatively affects women

more than children and men (King and McCarthy, 2009). Children have sensitive receptors and

are significantly inclined to develop mental retardation, kidney damage, or behavior problems

because of lead. Nevertheless, parents also have the potential of obtaining the harmful effects of

lead as well because fathers in the lead smelter communities are the individuals who work within

the facility that causes the contamination of lead while women have the burden of responsibility

over children since most have adopted housewife lifestyles (King and McCarthy, 2009). Public

health authorities have published handbooks and posters to residents describing how and what

should be done about the spread of lead contamination in households while specifically targeting

children (King and McCarthy, 2009). The proposals public authorities have made are skewed

due to its diversion from the legitimate problem, the smelters. Some responsibilities households

have in Boolaroo are to use diluted mops instead of brooms to clean lead dust multiple times a

day, constantly alert children not to put toys in their mouths, keep dust out of the presence of

children, under beds, closets, corners, behind furniture, and doors (King and McCarthy, 2009).

There are also directives, mainly for housewives, to stop children from sucking their own

fingers, wipe surfaces before preparing food, and to cover food and eating utensils from lead dust

(King and McCarthy, 2009).Women in the Boolaroo community have the burden of shame, fear,

and anxiety when the result of their continuous efforts to have successful housekeeping fails

along with the consequent unhealthy development of their children (King and McCarthy, 2009).

Most people in contemporary America own a cell phone, a computer, or a car, but

disregard the issues behind its production. Many Americans value the convenience of

communicating with one another while being hundreds of miles away from each other with the

utilization of cell phones. At the end of 2006, there were over 233 million cell phones in use and

its average life is about 18 months, which equates up to 150 million phones needed to be

replaced per year (Mireille, et al 2006). As population continues to increment, renewal, disposal,

and production of new cell phones will run parallel with the increase. “Cell phones will be

thrown away at a rate of 130 million a year by 2005, that equals 65,000 tons of waste containing

toxic metals”(Recyclemycellphone.org, 2010). Heavy metals that were listed above may be

incinerated at the end life of a cell phone and creates flue gas, fly ash, and bottom ash that

disperse into the air, water, and soil, or may be landfilled. In the landfill, heavy metals leach and

seep down into soils and eventually reach aquifers (Lim and Schoenung 2010). The end result of

improper disposal of cell phones is harm to human health and ecosystems in the result of air,

water, and soil contamination. Given most predicaments behind cell phones, it must raise

concerns for developing countries because the norm in developed countries is to have a cell

phone due to global consumption patterns (Mireille, et al 2006). Cell phones are almost a

necessity in developed countries such as the United States and in turn, this behavior is being

copied in developing countries where there are no proper waste management practices being

implemented (Diamond, 2005).Cell phones can be applied to electronics as a whole because

most accessories such as computers and stereos contain lead which would reciprocally affect

residents near lead smelters like in Boolaroo, Australia (EPA, 2010).

Nonetheless, if heavy metal soil contamination exists, there are scientific solutions to

toxic ordeals. Bioremediation may be used to battle toxins in soils because it “is a technique that

uses living organisms in order to degrade or transform contaminants into their less toxic forms”

(Kavamura, Esposito, 2010). Phytoremediation uses the same principles as bioremediation

except it is organism specific because of its utilization of plants or fungi (Kavamura, Esposito,

2010). Rhizoremeditation is used to assist phytoremediation’s inability of cleaning multiple

pollutants simultaneously by using microorganisms to increase the efficiency for the extraction

of contaminants (Kavamura, Esposito, 2010).

Bioremediation has two methods of cleaning toxins in soils. The first is in situ, where

treatment is completed in the premises of the heavy metal contamination and ex situ takes place

outside the site by extracting the soil to treat it afterwards (Kavamura, Esposito, 2010).

Biosorption is an adhesive procedure in which metals bind with cell surfaces to have the results

of adsorption and desorption (Kavamura, Esposito, 2010). Adsorption is the assembly of a gas,

liquid, or substance into a thin layer and desorption is the removal of the absorbent

(Dictionary.com, 2010). A bacterium classified as Trichoderma reesei adsorp and

desorp cadmium and copper ions in soils and water. Another bacterium

labeled Amanita rubescens undergoes a process called bioleaching. Bioleaching is

a process some organisms go through in order to dissolve metal ions (Kavamura, Esposito,

2010). Amanita ruescens is an extraordinary organism because it has the ability to dissolve the

most destructive and harmful toxins, lead and cadmium.

Phytoremediation practices are similar to bioremediation except for the fact that plants or

fungi are specifically used to treat contaminants in soils. Therefore, a phytoremediation practice

called chelate assisted phytoextraction will be explained in detail instead. Phytoremediation with

chelate assisted phytoextraction is described as one of many methods that is being used to get rid

of adverse heavy metal chemicals from soils. Chelating agents enhance the solubility of heavy

metals in soils which subsequently aids the phytoextraction process of transfering metal

concentrations to harvestable areas of roots and surface shoots of plants (Garbitsu and Alkorta

2000). Only a selective number of plants are able to retain large traces of metals. The plants that

have the ability to do so are called hyperaccumulators (Garbitsu and Alkorta 2000). In order for

these species to be successful in removing a substantial amount of metals, they must fit many

requirements such as fast growth rate, deep roots, great biomass production, elevated tolerance to

the metals, quick uptake speeds, high reproductive feasibility, and easy gathering of the targeted

metal (Evangelou, Ebel, and Schaeffer 2007). Uptaking is the relocation of metal accumulations

to harvestable areas of roots and surface shoots of plants (Garbitsu and Alkorta 2000).

Unfortunately, hyperaccumulators do not qualify for many of the important success requirements

because of their slow growth and small bio mass production (Evangelou, Ebel, and Schaeffer

2007).

Non hyperaccumulators quickly grow and have a large bio mass production, but lack

metal accumulation and uptake speed (Evangelou, Ebel, and Schaeffer 2007). Therefore,

chelating agents have been introduced to certain plant species to enhance its natural occurrences

of metal accumulation and uptake speed. Chelating agents increase the removal of metals from

soil and increase the concentration of metals into a soil based solution. This augments the uptake

of metals within plants (Evangelou, Ebel, and Schaeffer 2007). Consequently, this enlarges

phytoextraction rates, but raises questions on which chelates and plants are most effective with

which metals.

There are two kinds of chelates or aminopolycarboxylic acids (APCAs) that are used to

help detoxify heavy metal contaminants; synthetic and natural. The most effective and

commonly used synthetic chelating agents for metals such as lead is diamine tetraacetic acid

(EDTA) with the combined use of the Indian mustard plant (Garbitsu and Alkorta 2000). When 3

mmol kg-1 of the agent was added to 23 fold plants available, approximately 26 fold of heavy

metal uptake in plants occured (Evangelou, Ebel, and Schaeffer 2007). Although quite

successful, synthetic chelating agents face many issues. EDTA’s decreased biodegradability

capabilities are toxic to soil microorganisms and plants which drastically decrease the biomass of

plant shoots, remain in soils even after cleaning, and its longevity escalate the chances of

leaching from heavy metals (Evangelou, Ebel, and Schaeffer 2007). On the contrary,

nitrilotriacetic acid is biodegradable, has a decreased rate of leaching metals because of its quick

decomposition through photodegredation depending on which metal being used, and has the best

heavy metal uptake for zinc and arsenic (Evangelou, Ebel, and Schaeffer 2007). Although the

exact numbers aren’t shown for arsenic Evangelou, Ebel, and Schaeffer 2007 states zinc had 20

mmol kg-1 of the agent added to 300-fold of plants available, and around 37 fold of heavy

metaluptake took place with the use of Corn and Vetiver grass. Regrettably, there was a biomass

decrease in the process of zinc (Evangelou, Ebel, and Schaeffer 2007).

Unfortunately, phytoremdiation practices are not as effective when variations of heavy

metal pollutants are in one area. On the other hand, rhizoremediation is an adequate resolution to

phytoremdiation’s flaws by inputting microorganisms in the treatment system (Kavamura,

Esposito, 2010). In rhizoremediation, microorganisms increase the accessibility of heavy metal

compounds, while the plant subsequently pulls and removes the compounds (Kavamura,

Esposito, 2010). This microorganism and plant relationship is beneficial for both parties because

plants provide nutrients for microorganisms to regenerate and multiply to increment the

extraction of heavy metal contamination (Kavamura, Esposito, 2010). Effective treatments of

cadmium and zinc have been made possible with the use of the Hebeloma fungi and the

bacterium Microccus leteus (Kavamura, Esposito, 2010). Approximately 53 percent of cadmium

and 62 percent of zinc were accumulated in the shoots of the fungi. Rhizoremediation is a new

procedure for remediation practice and needs to be explored to fully understand and gain

substantial results for other contaminants (Kavamura, Esposito, 2010).

Economic, political, sociological, and scientific comprehension and resolutions are

necessary when dealing with heavy metal soil contamination issues. In the circumstance of

Boolaroo, Australia, cap and trade programs for lead, strict facility regulations such as producer

responsibility for contamination, and relocation of residents to a safe area away from lead

smelters are possible means to achieve successful goals to reduce and eventually eliminate lead

contamination. Regrettably, toxic heavy metal constituents from marketable products create

environmental perils, and production and consumption issues. Therefore, effective world policies

of waste management needs to made because heavy metal soil contamination is a global

problem. A way to close open loops in the waste stream in relation to hazardous products is to

create local end-user markets that will keep the products in use rather than going to the landfill.

As for remediation practices, further research for the discovery of fully effective treatment is

pendant. Leaching of heavy metals in soils remains a prolonged predicament and perhaps an

amalgamation of chemicals that would stop or substantially reduce heavy metals from leaching

can be a temporary solution.

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