Drinking water in Gaza Strip contaminated with high levels of nitrate

Palestinian and German scientists have recommended to the authorities in the Gaza Strip that they take immediate measures to combat excessive nitrate levels in the drinking water.

90 per cent of their water samples were found to contain nitrate concentrations that were between two and eight times higher than the limit recommended by the World Health Organization (WHO), say the researchers from the University of Heidelberg and the Helmholtz Centre for Environmental Research (UFZ) writing in the specialist journal Science of the Total Environment. Over the long term they recommend that the best protection would be provided by quality management for groundwater resources.

Groundwater is the only source of drinking water for the majority of people living in the Gaza Strip. In babies younger than six months, nitrate can lead to methaemoglobinaemia, to diarrhoea and to acidosis. The WHO therefore recommends keeping nitrate levels to 50 milligrams per litre or less. According to unpublished research, half of the 640 infants tested were already showing signs of methaemoglobinaemia.

The new Palestinian-German study confirms earlier water analyses and is the first study to pinpoint a source of the contamination. With the help of isotope analyses, the researchers were able to demonstrate that the nitrate pollution can be traced back to manure used in farming and to wastewater.

With over 2600 people per square kilometre, the Gaza Strip is one of the most densely populated areas on earth. Because of their isolation, the inhabitants of this area between the Mediterranean, Egypt and Israel are reliant on being self-sufficient. The fields are mostly fertilized with chicken and cow dung. Artificial fertilizers account for only around a quarter of the fertilizer used. Because of the area’s geology and the semi-arid climate, it is fairly easy for impurities to seep down from the surface into the aquifier system.

Organic fertilizers and wastewater are the main causes of the nitrate contamination in the groundwater, followed by sewage sludge and artificial fertilizers. This was revealed by the isotope ratios of nitrogen (15N/14N) and oxygen (18O/16O) in the nitrate. Isotopes are variations of the same chemical element that have a different number of neutrons in their nuclei. 18O and 15N are stable, i.e. non-radioactive, isotopes that are heavier than “normal” oxygen (16O) or nitrogen (14N) and can therefore be measured using a mass spectrometer.

The lower 15N nitrogen isotope values in the sewage sludge indicate that the nitrate in the Gaza groundwater comes primarily from manure used as fertilizer,” explains Dr Karsten Osenbrück of the UFZ. Between 2001 and 2007 the scientists took water samples from 115 municipal wells and 50 private wells on seven occasions. They measured nitrate concentrations of between 31 and 452 milligrams per litre. Only 10 of the 115 municipal wells examined were found to have a nitrate level below the WHO guideline value. The situation with the private wells was equally serious: apart from three, all the wells were found to have nitrate levels that were between five and seven times higher than the WHO recommendations.