By Dr. Maibam Dhanaraj Meitei
Wetlands, one of the most important ecosystems on earth, are known as ecological supermarkets. Wetlands support extensive food chain and play a major role in the landscape by providing unique habitats for a range of flora and fauna. Loktak, the largest pat within the Manipur river basin serves as an important source of water, fisheries and vegetation providing sustenance to a large population. It has got a rich biodiversity of 233 plant species and 425 species of animals (249 vertebrates and 176 invertebrates). Loktak provides refuge to thousands of birds which belong to 116 species (21 species of waterfowl are migratory, most migrating from different parts of the northern hemisphere beyond the Himalayas).
Phoomdi is a heterogeneous mass of soil, vegetation and organic matter in different stages of decay. It occurs in various sizes, small or large with thickness varying from a few centimeters to above 2.5 m. Phoomdi is a habitat of a large variety of aquatic, semi-aquatic and terrestrial plants, comprising of more than 128 species from above 46 families. Communities living in and around the wetland are directly or indirectly dependent upon the wetland resources for sustenance. There is a significant population which harvests aquatic plants from Loktak for different purposes. It has been estimated that 33% of the wetland shore households harvest aquatic vegetation for use as fuel; 18% for use as vegetables; 2% for use as fodder and 1% for manufacturing handicrafts. Annually, 15,400 MT of plant biomass is harvested for use as fuel, 1,900 MT for use as vegetables, 230 MT for use as fodder and 40 MT for making handicrafts.
However, wetland plants are reported to have a comprehensive capacity for the accumulation of numerous heavy metals. Because of their fibrous root systems with large contact area, they have the ability to concentrate higher amount of metals than the surrounding water. At present, Loktak is exposed to excess silts load, nutrients, pesticides and metals, quickening its ageing. Loktak Multipurpose Project (1983) converted the wetland with fluctuating water level into a reservoir with more or less constant water level; compounding the deposition of nutrients, metals and silts by interfering with the wetland hydro-dynamics and flushing of pollutants. Further, lack of proper sanitation actions in the Manipur valley generates near to 77.13 million tons of solid waste and 33,148 m3 of sewage on a daily basis by 0.28 million people living within the Nambul river.
Phoomdi includes plants that accumulate numerous heavy metals. A study (Singh et al. 2013) compared the concentrations of metals between Loktak and the Nambul River, a main tributary. Metal concentrations were found to be higher in the Nambul River than in Loktak, viz. 1966.7/468.4 (Mn), 1486.5/646.2 (Fe), 244.8/45 (Zn), 5.5/3.7 (Cr), 2/1.4 (Ni) and 3/0.8 (Hg) ppb. These results signify the possible role of sediments and phoomdi acting as sinks and accumulators. Further, another research (Meitei and Prasad 2016) reports the concentrations of Fe, Mn, Zn and Cu in the sediments of Loktak ranged upto 81.8 ± 0.45 – 253.1 ± 0.51; 2.6 ± 0.06 – 71.9 ± 0.34; 0.13 ± 0.006 – 0.43 ± 0.107 and 0.02 ± 0.001 – 0.09 ± 0.002 mg kg-1, respectively. Wetland sediment enhanced with organic matter work as a potential good sink for numerous metals compared to surface water (Fe, Mn, Zn and Cu ranged upto 81.8 ± 0.45 – 253.1 ± 0.51; 2.6 ± 0.06 – 71.9 ± 0.34; 0.13 ± 0.006 – 0.43 ± 0.107 and 0.02 ± 0.001 – 0.09 ± 0.002 mg kg-1), as the humic substances existing in sediment create various metal complexes. However, a relative low metal concentration in water is ascribed to their constant uptake by phoomdi during growth and development.
As the wetland function as a drinking water source, low metal concentrations sustained by phoomdi acts as a safe defense for the health of the locals and environment of Loktak. However, a study (Meitei and Prasad 2015) reported a total of 27 wild edible and 25 medicinal species used by the locals from phoomdi. Target hazard quotient, proposed by the US Environmental Protection Agency (US EPA) has been recognized as one of the reasonable indexes for health risk evaluation associated with the intake of metals by consuming contaminated food. THQ < 1 suggests that the exposed population is safe from the harmful effects via the consumption of the contaminated food and 1 < THQ < 5 means that the exposed population is in a level of concern interval.
In a report (Meitei and Prasad 2016), it is observed that the THQ values of Mn were higher than Fe, Zn and Cu for the 7 phoomdi edibles (Alternanthera philoxeroides, Ipomoea aquatica, Colocasia esculenta, Trapa natans, Zizania latifolia, Oenanthe javanica and Polygonum barbatum) from Loktak. Target hazard quotient values of Zn and Cu for phoomdi wild edibles was below 1 ranging from 0.02 – 0.09 and 0.01 – 0.04 respectively, suggesting that consumption of the wild edibles are safe from the toxic effects of the metals (Zn and Cu). For Fe, THQ values ranged from 0.2 – 1.5; with higher values for Zizania latifolia (1.5), Oenanthe javanica (1.3) and Polygonum barbatum (1.1); signifying the necessity for care to be paid. Similarly, maximum THQ value of 7.9 for Mn was found in Alternanthera philoxeroides, followed by 2.3 for Polygonum barbatum and 2.1 for Trapa natans, respectively. Relative high THQ of Mn showed that the contamination of the metal in the phoomdi wild edibles might pose a potential health hazard.
On the contrary, the mentioned phoomdi wild edibles are a common constituent of the local meal every day. Fresh vegetables are used to prepare Manipuri traditional delicacies, viz. iromba, kangsoi, kangsu, shak, singju, and utti. Iromba is prepared by boiling Alpinia nigra, Colocasia esculenta, Hedychium. coronarium, chilli and potato. Boiled vegetables are mashed and mixed with fermented fish. Tender shoots of Ipomoea aquatica are boiled with potato, fish and spices in the preparation of shak. Singju is a salad made by mixing Alocasia cucullata, Ipomoea aquatica, Neptunia oleracea, Oenanthe javanica, and Polygonum barbatum, with fermented fish and chilli. Alternanthera philoxeroides and Colocasia esculenta leaves are used in utti. They are boiled with green peas, chillies, spices, fermented fish and sodium bicarbonate, etc.
There arises the concern, as the phoomdi of Loktak are interconnected in many ways with the common life of the locals that environs the surrounding of the wetland. Harvesting and consumption of the phoomdi wild edibles will lead to the transfer of heavy metals to the human due to metal contamination. High amounts of Fe are reported to cause hemorrhagic necrosis, tissue injury by catalyzing the conversion of H2O2 to free radical ions and can activate oncogenes. Also, excessive accumulation of Mn leads to neurological disorders and brain damage. Further, Zn at high concentrations can cause muscular stiffness, loss of appetite, nausea and irritation, and high Cu lead to metal fume fever, fair skin discoloration, irritation of the upper respiratory tract, dermatitis and nausea etc.
Thus, an in-depth research with constant observation and development of counter actions is required for public health interests of the locals that environ Loktak in the long run. Government of Manipur along with its responsible wing, Loktak development Authority needs to pay a serious attention to look upon and try solving or minimizing the various possible threats that haunt the locals and the wetland – Loktak.
The author is a resident of Kyamgei Maning Leikai, Imphal, Manipur and can be contacted at maibam(dot)meitei(dot)yahoo(dot)in