(477h) Dynamics, Source Diagnosis, and Risk Assessment of Persistent Organic Pollutants in Water and Sediments of the Urban Aquatic Bodies

Abstract:

Organic compounds which are persistent, posses toxic characteristics, liable to bioaccumulate, prone to long range atmospheric transport and can cause adverse environmental and human health effects at locations near and far from their sources can be defined as persistent organic pollutants (POPs). Polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) are the two important categories of POPs which are highly toxic to human beings, animals and plants. Polycyclic aromatic hydrocarbons are the product of any combustion process involving materials containing carbon and hydrogen namely coal, oil, petrol, wood etc. Emissions from the anthropogenic activities predominate, but some PAHs in the environment arise from natural combustion such as forest fires and volcanoes. PAHs occur naturally in crude oil and form a significant component of the petroleum products such as paints, creosote (used in wood preservation) and asphalt (used for road paving). There are some minor biogenic sources like plants, algae/phytoplankton and microorganisms and small amounts are formed by diagenesis in the lake sediments.

Organochlorine pesticides comprise a group of structurally diverse compounds with a large number of chlorine atoms. These pesticides have a tendency to bioaccumulate in the food chain and pose a great threat to the human health and the global environment. In spite of the ban on their use they are still being used in some of the developing countries, especially in the tropical regions, for health, agriculture and preservation purposes. Pesticides that are not bound in soils or taken up by the plants and animals can drain into rivers and lakes and move into the aquatic food chain.

The lakes and the rivers are two important types of surface water systems containing only 0.3% of the total global fresh water which is generally used for drinking purpose. These surface water resources, therefore, are precious and extremely sensitive and once degraded it would take immense efforts to revive them. In view of the above water and sediment samples were collected from two different types of urban surface water bodies of India.  One of the water bodies is a lake system of Bhopal (Madhya Pradesh-a central state of India) and the other body is the stretch of river Yamuna at Delhi-the capital city of India. The aquatic systems under investigation are the typical urban aquatic systems and exist in the densely populated areas. Both of the systems are in different geographical locations. These surface water bodies being urban are expected to suffer with some similar types of anthropogenic activities. The various types of industrial, agricultural and domestic activities in the catchment area create different level of anthropogenic stress.

For the extraction of PAHs from water and sediment samples the method followed by Chen et al. [1] was adopted. The mobile phase was a gradient of acetonitrile and degassed water (50% acetonitrile held for 7 min; linear gradient to 80% acetonitrile in 7 to 20 min; 80% acetonitrile held till 25 min and linear gradient to 95% acetonitrile from 25 to 30 min) at a flow rate of 1.5 mL min^-1. The analysis was carried out at 254 nm and the individual PAH was identified and quantified by comparing the retention time and peak area with those of the standards. The procedure for extraction and cleanup of OCPs from both water and sediments is the same as outlined by Wan et al. [2]. The mobile phase was acetonitrile and water (70:30) with isocratic mode and a flow rate of 1.3 mL min^-1. The analysis of aldrin, endrin, pp'-DDT and α-endosulfan was performed at the wavelength 220, 228, 238 and 214 nm, respectively. The individual pesticide was identified and quantified on the basis of retention time and peak area. PAHs and OCPs were analyzed with HPLC equipped with a UV-detector (Agilent 1100, USA) and recorder. An octadecyl endcapped RP-C₁₈ column (4.6 mm×250 mm, 5 µm particle size) was used.

The total PAHs (∑PAH) concentration in the water of the lakes and the river ranged from 4.85 to 18.2 ng/mL and 0.29 to 46.2 ng/mL, respectively. The profile of individual PAH in the water of both the aquatic systems is similar but different in sediments. The total PAHs concentration in sediments ranged from 952 to 5353 ng/g and 649 to 7910 ng/g for the lakes and river, respectively. The maximum pesticide concentrations in water and sediments of the lakes were 4.12 (aldrin), 2.26 (endrin), 6.17 (pp'-DDT), 5.98 ng/mL (α-endosulfan) and 167 (aldrin), 124 (endrin), 513 (pp'-DDT), 349 ng/g (α-endosulfan),  respectively. The aldrin and endrin were absent at all the sites of the Yamuna. The maximum concentration of pp'-DDT and α-endosulfan in river water was 3.37 ng/mL and 3.55 ng/mL and in sediments 525 ng/g and 194 ng/g, respectively.

A perusal of the data points out that certain areas of the two aquatic systems are severely contaminated with PAHs and pesticides. The ∑PAH concentrations in water at some points of the lake system are above the lethal concentration and may cause acute toxicity to the exposed organisms. The data in the case of river indicate that both water and sediments are highly contaminated with PAHs. In both the cases the source of PAHs is mainly pyrogenic in nature.  The potential toxicity due to total PAH concentrations will be rare in the lake system. The scenario is totally different in the case of river sediments where at most of the sites the toxic effects will be occasional. The apparent reasons for the deterioration of the said water bodies due to PAHs are dumping of untreated waste and a common practice of open burning of a variety of solid waste on the banks of the aquatic bodies. Apart from this, localized activity like plying of diesel operated motor boats is also contributing to the PAH pollution in the lake system. The major contributing activities responsible for PAHs contamination to the river through surface runoff and atmospheric transport are thermal power plants, heavy vehicular traffic load and domestic and industrial waste. A comparison of the two aquatic systems under study indicates that the ∑PAH concentrations in the river are about two times higher than those detected in the lakes. The PAH profiles in the water of the two systems are similar but the profiles in the sediments are different.

As far as the contamination due to pesticides is concerned aldrin is detected only at a few sites of the lake system and the other pesticides are observed only at sites surrounded by agricultural land. Endrin, pp'-DDT and α-endosulfan, wherever detected in water, are generally above the prescribed limit of acute toxicity. Aldrin and endrin are not detected in water and sediments of the river. Both the water and the sediments of the river are heavily contaminated with α-endosulfan and pp'-DDT. The biological impairments due endrin in the lakes and pp'-DDT in the river will be frequent as their levels in the sediments are above PEL. The accumulation of pesticides in the sediments may affect the natural bacterial composition and can lead to anaerobic conditions which may result in more toxic byproducts such as sulfide and ammonia.

References:

[1]. Chen, B., Xiaodong, X., Lizhong, Z., Jing, W., Yanzheng, G., Kun, Y., Xueyou, S. and

         Baofeng, L., “Distributions of polycyclic aromatic hydrocarbons in surface waters,

         sediments and soils of Hangzhou City, China”, Water Res. 38, 3558 (2004).

[2]. Wan, M.T., Kuo, J. and Pasternak, J., “Residues of endosulfan and other selected

         organochlorine pesticides in farm areas of the lower Fraser valley, British Columbia,     

         Canada”, J. Environ. Qual. 34, 1186 (2005).