Physico-Chemical and Heavy Metals in the Groundwater Samples Collected from Arsenic Endemic Areas of Shuklaganj (Unnao)

Human health is greatly affected by exposure to arsenic through drinking water. Arsenic is a carcinogen and its consumption can negatively affect the gastrointestinal tract, card io-vascular and central nervous systems. World Health Organisation (WHO) and US Environmental Protection Agency have set the maximum acceptable level of arsenic in drinking water as 10μg/L. Attempts have been made to determine and establish a database on the drinking water quality of Shuklaganj area with part icular emphasis on the physico-chemical characteristics and levels of heavy metals in the water samples. The physico-chemical parameters determined were pH, hardness, alkalin ity, conductivity, TDS, salinity and ch loride content. The samples were collected in premonsoon and postmonsoon of Shuklaganj area. The pH of all the samples varied from 7.0 to 8.5 in both premonsoon and postmonsoon period. Hardness during in premonsoon varied from 180-212mg/L and in postmonsoon varied from 140-210 mg/ l. Alkalinity varied from 84-112mg/L in premonsoon and 60-128 mg/L in postmosoon. However conductivity was quite high and it ranged from 320-2140 μs/cm in premonsoon and 358-1944μs/cm during postmonsoon. The TDS ranged from 181-1019 mg/l in premonsoon samples and 163-1102mg/l in postmonsoon. Salinity varied from 0.0-1.0 ppt in premonsoon and 0.0-1.3 ppt in postmonsoon. Chloride content varied from to 12.1-36.4 in premonsoon and 8.08-44.5 mg/L in potmonsoon. The p icture of heavy metals and arsenic present in the water collected during premonsoon and postmonsoon periods were also determined. However, in premonsoon samples Cr, Cd and Ni were absent in most of the samples. It was noticed that Cd and Ni content was almost absent in the samples collected during postmonsoon season. Copper varied from 0.0 to 0.0178 mg/L during premonsoon and 0.0002 to 0.0098mg/L during postmonsoon. Zinc content varied from 0.0 to 3.26 in p remonsoon period and from 0.0-3.6 mg/L in postmonsoon period. Iron varied from 0.0 to 17.99 mg/L in pre monsoon and varied from 0.0692 to 12.53 in postmonsoon samples. Manganese varied from 0.0 to 0.4454 mg/L in premonsoon samples and 0.00184.74 mg/L in premonsoon samples. Arsenic in premonsoon season varied from 0-250 ppb and from 0-250 ppb in postmonsoon. It is seen that with increase in pH above 8.5, Arsenic desorbs from the oxide surfaces, thereby increasing concentration of Arsenic in solution. It is suggested that the most desirable and significant mechanism for the groundwater Arsenic problems is due to oxidising conditions and desorption of Arsenic from Arsenic contaminated sediments at high pH.


Introduction
Hu man health is greatly affected by exposure to arsenic through drin king water. Arsen ic is a carcinogen and its consumption can negatively affect the gastrointestinal tract, cardio-vascular and central nervous systems. World Health Organ isat ion (W HO) and US Env iron mental Prot ect ion Agency have set the maximu m acceptable level of arsenic in d rin k in g water as 10 µg / L [ 1,2 ]. A rs en ic o ccu rs in groundwater primarily as a result of natural weathering of arsenic containing rocks, although in certain areas high arsen ic co ncen t rat io n are caused due to indust rial waste discharges and application of arsenical herbicides/pesticides [3]. Arsenic is present in water mainly in the forms of arsenate As (V) and arsenite (As III). In the environmentally relevant pH range 4-10, the do minant As (V) species are negatively charged (H 2 AsO 4 2-), while the dominant As (III) species is neutrally charged (H 3 AsO 3 ).
Arsenic is introduced in the soil and groundwater during weathering of rocks and minerals followed by leaching and runoff. Also it can be introduced in soil and groundwater fro m anthropogenic sources. Many factors control Arsenic concentration and transport in groundwater which include Redo x potent ial, absorption/desorption/precipitation/dissolu tion. Arsenic groundwater has far reaching consequences including its ingestion through food chain, which are in the form of social disorders, health hazards and socioeconomic dissolution besides its sprawling with movement and exploitation o f groundwater. The food crops which are grown using arsenic contaminated water are sold off to other places, includ ing contaminated regions where the inhabitants may consume arsenic fro m contaminated food. This may give rise to new danger.
It is well known that trace elements of Arsenic is both advantageous to plant and animal nutrition [4,5,6], but there are no reports of this type in humans [7]. However, h igher levels of Arsenic are found to be harmful to hu mans. The contamination of Arsenic of surface and groundwater occurs world wide and has become a sociopolitical issue in several parts of the globe. For examp le, there are lots of people who are at risk of drinking As-contaminated water in West Bengal (India) [8,9] and Bangladesh [10]. Sco res of people fro m China [11], Vietnam [12], Taiwan [13], Chile [14], Argentina [15], and Mexico [16] are likely at risk as well. Skin manifestations of many types and other arsenic toxicity were observed fro m melanosis, keratosis, hyperkeratosis, dorsal keratosis, and non pitting edema to gangrene and cancer. Overall, prevalence of clin ical neuropathy was noticed in various studies in populations of 24-Pargana-North, 24-Pargana-South, Murshidabad, Nadia, and Bardhaman districts of West Bengal and in the states of Bihar, Uttar Pradesh, Jharkhand and Chhattisgarh. Adults are less affected due to arsenic than children. Most of the population suffering fro m arsenic skin lesions is fro m a poor socio-economic background and adults are less affected to arsenic than children. Albertus Magnus in 1250 AD for the first time documented the hazardous effects of Arsenic . The hazardous effects of Arsenic on both flora and fauna are well known [17]. The consumption of arsenic contaminated water is the main path for its transportation into the environment and biological systems [3,18,19,20,21] is also well known. Attempts have been made to determine and establish a database on the drinking water quality of Shuklaganj area with particular emphasis on the physico-chemical characteristics and levels of heavy metals in the water samples.  The data is the mean of three samples collected from each source (N=3)

Materials and Methods
Drinking water samp les were collected fro m India mark II handpumps in and around Shuklaganj area. Samp les for physico-chemical analysis were collected in plastic sterilized bottles and transported to the laboratory. Before filling the samples these bottles have been rinsed two or three times with water. The record of every sample is maintained by an appropriate labelling including the name of the samp le collector, the date , timing and exact location. Identification of the sites was made by recording the co-ordinates using the GPS. The samples were co llected in premonsoon and postmonsoon of Shuklaganj area. For analysis of metals the water samples have been collected in glass or plastic (polyethylene) bottles and 2.0 ml of n itric acid is added in each bottle. All the samples have to be stored at 4 0 C for storage and analysis. For quantitative metal analysis a mu lti-elemental standard solution of Cu, Cr, Cd, Zn, Fe, Mn, Ni, As was collected in 2% nitric acid co mmercial 1g/L. Individual standard solution was stored in polyethylene bottles. Measurement was made on Inductivity Couple Plas ma (ICP) Instrument (Thermo Electric Corporation Intrepid II x DL) with axial viewing configuration. The complete process of sample preparation and analysis of physico-chemical and metals was made as per the standard methods [22].

3.Results and Discussion
The physico-chemical parameters and the GPS location of the water samples collected in and around Shuklaganj area are shown in Table1   The data is the mean of three samples collected from each source (N=3) The picture of heavy metals and arsenic present in the water co llected during premonsoon and postmonsoon periods were also determined and are shown in Table 4 stable [23,24,25]. The speciation of As in aquatic environ ment is crit ical in controlling the adsorption/desorpti on reactions with sediments. Adsorption to sediment particles may remove As(V) fro m contaminated water, as well as inhibit ing the precipitation of As minerals such as scorodite (FeAsO 4. 2H 2 O) that control the equilibriu m aqueous concentration [26]. Under the aerobic and acid ic to near-neutral conditions (typical of many aquatic environments), As(V) is adsorbed very strongly by oxide minerals in sediments. The highly nonlinear nature of the adsorption isotherm for As(V) in o xide minerals ensures that the amount of As adsorbed is relatively large, even when dissolved aqueous concentrations of As are low. Such adsorption occurring in natural environments protects water bodies from widespread As toxicity problems. Adsorption of As species by sediments are as follows: As(V) > As(III) > As (II) > DMA [3]. In As-contaminated sediments, Clement and Faust (1981) [27] found that a significant portion of the As was bound in organo-complex forms and indicated that adsorption-desorption equilibriu m must be considered as well as the redo x effects in examining the dynamics of As in aquatic environment.

Conclusions
It is seen that with increase of pH above 8.5, Arsenic desorbs fro m the oxide surfaces, thereby increasing the concentration of As in solution. It is suggested that the most desirable and significant mechanism for the groundwater As problems due to oxidizing conditions and the desorption of As from As contaminated sediments at high pH [28,29].  The data is the mean of three samples collected from each source (N=3)