WATER QUALITY AND RESIDUALS OF NITRATE - NITRITE IN SOME VEGETABLE PLANTED IN CEMETERY AT THANH TRI DISTRICT, HANOI, VIETNAM

Abstract

Vinh Quynh commune, Thanh Tri district, Hanoi is well-known for one of the places that provides a lot of vegetables for Hanoi people, but the vegetables growing near the cemetery area contain numerous of hidden risks. To assess water quality and the residuals of nitrate and nitrite contents in three types of vegetables: Ipomoea aquatic, Nasturtium officinale, and Oenanthe javanica, the study took 12 surface water samples to analyze pH, TSS, COD, NO₂^-, Fe, NH₄⁺, PO₄^3- and NO₃^- and 10 groundwater samples for analyzing pH, Fe, NO₂^-, PO₄^3- and NO₃^-. In addition, 16 vegetable samples (10 samples of water spinach, 3 samples of watercress, and 3 samples of water dropwort) were collected to analyze nitrate and nitrite concentration in vegetables by a method of extraction and chemical color. The main results of the study included: (1) The surface water was polluted in  Fe, PO₄^3-, NO₂^-, NH₄⁺, COD, TSS and NO₃^-  whereas groundwater was polluted in 4 indicators: Fe, PO₄^3-, NO₂^-, and NO₃^-. Especially, NO₃^- and PO₄^3- had the highest concentration which exceeded 18 times permitted level for surface water sample nearest distance to the cemetery. The WQI index of groundwater was very poor at 208.5. Pollution of groundwater may be due to the infiltration of pollution sources from surface water. Typically, the correlation index of NO^3- concentration in surface water and fresh water is very high (r = 0.972); (2) All types of vegetables had NO₃^- concentration exceeded the permitted levels of WHO and EC. Vegetable sample located nearest the cemetery had the highest NO₃^- contents were 742 and 728 mg/fresh-kg, surpassed 2.5 times the safe level, respectively.