Study of groundwater quality in the region of Strumica, an important irrigation resource in the agriculture production

Groundwater quality in the region of Strumica was investigated in the period between 2013 – 2015. Around 76% of boreholes have depths of up to 23 m and the remaining 24% have depth from 70 to 130 m. Groundwater is slightly alkaline and have an average temperature of about 16,5 ºC. Conductivity is in the range from 1,22 to 17,49 μS/cm and alkalinity from 0,05 to 750,97 mg/l. Major ions in groundwater are Ca2+ and HCO3 –, suggesting that they lay on karst which is the main reason for their alkalinity and alkalinity of the soil as well. Al, As, B, Be, Cd, Cr, Co, Cu, Fe, Pb, Li, Mn, Mo, Ni, V, Zn, Ti are qualitatively and quantitatively determined using mass spectrometry with inductively coupled plasma (ICPMS) on an Agilent 7500 CX. Concentrations exceeding the MCL values according to the Regulation of waters in RM and FAO were found for NO3 –, As, Mn, Cl and Mo in 34,45% 15,13%, 88,5% and 47,70% of the samples. Groundwaters from the prolluviual part of the valley are found to be more voulnerable to nitrate pollution in relation to grounwaters from alluvial part of the valley where chemical caracteristics suggests the occurrence of denitrification. Statistical analysis showed that heavy metals and trace elements probably origin from the rock formation of the aquifers and the geology of the region. Thirteen of the most used pesticides were investigated in this study: buprofezin, benalaxyl, methomyl, metribuzin, malathion, pyrimethanil, pirimicarb, propamocarb, pirimiphos methyl, penconazole, triadimenol, chlorpyrifos, and -cyhalothrin. The use of liquid liquid extraction with dichloromethane (DCM) as a solvent from aqueous matrix, can be used for the extraction of all investigated pesticides except for the pesticide propamocarb. Gas chromatography coupled with mass spectrometry (GC-MS) was done on an apparatus Agilent 6890N coupled to a mass spectrometer and equipped with JAS UNIS split/splitless injector series 7683B. Glass wool liner type (JAS 90323L) with single restriction, 88 mm long and 3 mm ID, was used in all experiments. For the separation of analytes DB-5ms Supelco column was used with helium as a carrier gas. A research has been done in order to investigate the most suitable pressure in the injector that could improve the visibility of the signal. The result show that pulse pressure of 50 psi and purge flow vent of 1,5 minutes improves the signal of methomyl but the pure flow vent of 0,5 minutes improve the signal of chlorpyrifos and malathion. Pressure of 10 psi and purge flow vent of 0,5 minutes improves the signal of pyrimethanil, penconazol, pirimicarb and metribuzin. When the preassure is 20 psi and the purge folw vent is 1,5 minutes the improvement was noticed for pirimiphos methyl and benalaxyl. Even though the investigated region was considered to be vulnerable for the presence of pesticides, only 5% of the investigated 78 samples showed the presence of pyrimethanil and chlorpyrifos at concentrations of 0,0299 ± 0,00026 μg/l and 0,0133 ± 0,00929 μg/l, respectively. The main reason for this is considered to be the greenhouse production and the dropping irrigation system which doesn’t allow high quantity of water to be able to pass from the surface to the aquifers. Kew words: pesticides, heavy metals, nitrates, GC - MS, ICP - MS