This is a solution of environment study assignment in which we discuss Hexachlorobenzene (HCB) has been used in industries and agriculture since a long time.
Use of Hexachlorobenzene (HCB)
Hexachlorobenzene (HCB) has been used in industries and agriculture since a long time. HCB was earlier used as a fungicide as a counter-measure against diseases such as bunt for wheat, barley, oat and rye crops. It has also been applied as dressing material to seeds of onions and sorghum in US and many European countries. However, the pesticide and fungicide use is now discontinued in many countries due to health concerns arising from the toxic properties of HCB. HCB has also been used as a wood preserving agent, porosity-control agent in the manufacture of graphite anodes, as a peptizing agent in the production of nitroso and styrene rubber for tyres, in the production of pyrotechnics and tracer bullets for the US and Russian military, as a fluxing agent in the manufacture of aluminum, and as a chemical intermediate in dye manufacturing (Barber, Sweetman and Jones, 2005). Nowadays, HCB has hardly any commercial applications in US and Canada, but is still used in pyrotechnical compounds in the Russian Federation. Production of HCB has been banned globally under the Stockholm Convention on persistent organic pollutants (USEPA, 2002).
HCB as POP
HCB has been reportedly classified as a human carcinogen. Ingestion of crops treated with HCB is the cause of photosensitive skin lesions, hyperpigmentation, severe weakness, porphyrinuria, and debilitation in people, who later developed disorder of hemoglobin biosynthesis. These effects of HCB also passed through maternal milk from mothers to children, who developed pink sores with a mortality rate of 95%. Exposure to HCB also produces adverse effects on the reproductive tissues, and changes the enzyme activities and liver morphology of the animals. HCB also causes toxicological effects within aquatic life-forms (USEPA, 2002).
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HCB as a pollutant is also very persistent. Aerobic and anaerobic degradation process of HCB has estimated half-life approximately between 3-23 years. As a result of this persistence combined with the high partition coefficient, HCB concentrates itself biologically to high levels within living organisms. HCB is also easily transported over long ranges, due to its high stability and semi-volatility, such that traces of HCB have also been found in Arctic water and air life-forms (Barber, Sweetman and Jones, 2005). HCB is omnipresent, and is found in a variety of food samples ranging from pork, lamb and beef meat products. Surveys done have also revealed presence of HCB in pasteurized milk, oil and pulses samples; and certain monitoring programs have reported presence of HCB residues in aquatic foods such as; fish, prawns and caviar (USEPA, 2002).
Although, emission and production of HCB has been discontinued in many countries, it is still being generated as by-products of chemical processes such as manufacture of chlorinated solvents, chlorinated aromatics and pesticides. These wastes need to be managed or disposed using municipal waste treatment plants or through processes such as incineration. Much of the increasing environmental levels of HCB originate through sediment and soil. HCB losses from air are generally insignificant, and losses from water are of not much importance (Barber, Sweetman and Jones, 2005).
Need for global conventions to reduce pollutants.
With the globalization of shipping during the 1970s, there was an increased trading movement of hazardous waste and the disposal costs were skyrocketing. Several cases were reported where carriers carrying hazardous waste were involved in accidents, leading to spilling of hazardous waste into the environment and endangering nearby life-forms. As a result, developed nations decided to tighten environment laws and realized a need for a globally acceptable and applicable treaty to control and monitor safe movement of wastes across borders.
The Basel Convention: To restrict the movement of hazardous waste across nations, the Basel Convention was introduced on 22 March 1989, and was implemented with effect starting from 5 May 1992. Basel Convention is a global treaty which aims at minimizing the amount and toxicity of wastes generated, and assists less developed nations in managing the hazardous wastes generated by them. The convention intended reduction in waste production and obliged the participating nations to keep their wastes within their boundaries and as close as possible to the source of waste generation, by labeling waste trafficking as an illegal activity. The Basel Ban Amendment was introduced at the Basel conference of 1995, following the disagreement between many nations and NGOs who advocated total ban on shipment to the less developed nations. The Amendment was aimed at prohibiting all sorts of export of waste from developed countries to developing countries, including recycling.
The Rotterdam Convention: The Rotterdam Convention, highlighting the procedure liable to prior consent for trafficking of certain hazardous chemicals and pesticides in international trade, was introduced on 10 September 1998 and was successfully brought into force starting 24 February 2004. It is a global treaty aimed at promoting shared responsibilities regarding import and export of hazardous chemicals labeled as pollutants. The treaty calls for open exchange of information between exporters and promotes appropriate labeling of hazardous chemicals, including directions for safe handling and information to the importers regarding any restrictions or bans. Five new categories of substances have been proposed for inclusion in the treaty, and will be added to the amendments in the near future (UNEP).
The Stockholm Convention: The Stockholm Convention is an international treaty introduced in 2001 and entered into force in 2004. The aim of this is treaty is to protect human health and environment from persistent harmful pollutants that affect the well-beings of existing life-forms in the environment. According to the convention, the participating nations are required to eliminate or reduce POPs which cause cancer and diminished intelligence, and have the potential to transfer themselves over large distances. The treaty prohibits the use, production and import of POPs, and encourages parties to support the convention in all possible financial and scientific ways by identifying contaminated areas and providing incentives. Initially, the convention classified 12 chemicals as POPs, and aimed at completely eliminating their production and use. Since the May of 2009, the Convention started adding new substances to the agreement and intends to continue this trend in the future.
Methylmercury in marine environment
Methylmercury (MeHg) is a toxic organic substance found predominantly in fish tissue. Exposure to MeHg contaminated substances puts the human nervous system at risk, especially developing fetuses and young children. For adults, MeHg is said to cause cardiovascular diseases which may lead to heart attack. At higher concentrations it is also known to be a potent neurotoxin. Therefore, it is important to research MeHg in marine ecosystems for a better understanding of processes that regulate the bioaccumulation of MeHg in those systems (Chen et al. 2007). Notable government agencies such as EPA, ATSDR, WHO and FDA have issued guidelines for regulating exposure to methylmercury (Schierow, 2006).
Agency Level of Daily Exposure Level in Beach Resin
EPA 0.1 µg/kg/day 0.3 ppm
ATSDR 0.3 µg/kg/day –
FDA 0.42 µg/kg/day 1 ppm
The most common method for determination of methylmercury in environmental samples is gas chromatography (GC). Coupled with electron capture device (GC-ECD) or mass spectrometer (GC-MS), gas chromatography is used to separate methylmercury by converting it into alkyl or aryl mercury halides. This mercury halide is extracted into an aqueous cysteine complex in the form of mercury cysteine complex, and then extracted into benzene by acidification. It has been observed in the GC-MS studies that repeated injections of MeHg into the samples causes improvements in the detection, with measured detection capability as low as 1 ng g-1. A development in this study was recently made with the introduction of a new alkylation process involving methylcobalamin. The resulting volatile MeHg species were analyzed with a purge-and-trap gas chromatography process in line with a Fourier transform IR spectrometer (PT-GC/FTIR). However, due to dependence of MeHg formation on multiple factors, the practical applicability of this method is still unclear (Morita, Yoshinaga and Edmonds, 1998).
Effect of organic carbon on lipophilic chemicals
Physiochemical properties of soils and sediment, such as organic carbon content, are highly influential in determining the availability of lipophilic chemicals in the environment. Studies show that there is a 21 to 45% chance of reduction in the availability of HCB when compared to that of sediment without any patterns of organic carbon content (Saghir et al, 2009). There are strong interactions between the sediment and the carbon content, which can be proven by the increased elimination of lipophilic chemicals with the increased organic carbon content of sediments (Lotufo and Landrum, 2001). Organic carbon content is the most important soil property regarding sorption processes that affect the availability of pollutants as well as their movements through the soil. Empirical relationships have been established between lipophilicity and organic carbon content. Clay to total organic carbon ratio of 60 was indicated for lipophilic chemicals such as o-chlorotoluene. Soils in hot climates (such as sandy soils in arid regions) have low carbon content, and it is observed that these soils, due to a low biomass production, have a reduced capacity for immobilizing less lipophilic chemicals. Therefore, the hazardous effects resulting from the movement of these lipophilic chemicals through groundwater are greatly reduced. Sorption of these chemicals to colloidal organic macromolecules with high carbon content plays an important role in transport in surface waters (Klein, 1998).
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Barber, J. Sweetman, A. and Jones, K. 2005. Hexachlorobenzene – Sources, environmental fate and risk characterization. Science Dossier. [online] Available at: http://www.eurochlor.org/upload/documents/document187.pdf [Accessed 13 April 2011]
Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and Their Disposal. [online] Available at: http://www.basel.int/text/con-e-rev.pdf [Accessed 13 April 2011]
Chen, C. Serrell, N. Evers, D. Feishman, B. Lambert, K. Weiss, J. Mason, R. and Bank, M. 2007. Meeting Report: Methylmercury in Marine Ecosystems- From Sources to Seafood Consumers. Environmental Health Perspectives. 116(12), pp. 1706-1709. [online] Available at: http://www.scribd.com/doc/8682952/Meeting-Report-Methylmercury-in-Marine-EcosystemsFrom-Sources-to-Seafood-Consumers [Accessed 13 April 2011]
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