In Kazakhstan there is still no universal systematic monitoring of persistent organic pollutants (Kholubek et al., 2012). Upon that, a number of pilot projects of initial assistance to the Republic of Kazakhstan on obligations under the Stockholm Convention on Persistent Organic Pollutants has given reasoned conclusion that the problem is urgent in the republic (Kholubek et al., 2012; Zhanadilov et al., 2015.; Shabanova et al., 2010). This primarily relates to areas exposed to intense pollution by agricultural pesticides.

Ecological problems of Akmola region is largely determined by agro-industrial specialization of the region. The main branch of the region specialization is the production and processing of agricultural products (76%), including grain production – 56.8%. Akmola region has the highest percentage of rural population – 54.8% (Investment opportunities of the region, 2017; Sydykov et al., 2004; Seitkasymova, 2015).

The industry of this region is represented by the gold ore, uranium extraction, pharmaceutical and chemical industry, machine building and production of building materials (Sydykov et al., 2004; Press service of the Prime Minister of the Republic of Kazakhstan, 2018).

The area is rich in land resources. The total area of agricultural land is 13,791.7 thousand ha, areas of natural pastures are wide and occupy 6592.5 thousand hectares, the arable land is about 7,100 thousand ha. Almost all arable lands use some insecticides, fungicides - substances that are long-persistent in the environment, accumulated in the soil, in bottom sediments of stagnant water (Ljunggren et al., 2014; Jepson and Law, 2016).

In addition, the territory of the region under study still keep in some places some pesticides in abandoned warehouses without recycling, that were applied since the middle of last century. Names, respectively, contents of some pesticides are no longer possible to determine without analytical tests.

Thus, the territory of Akmola region is subjected to intensive human impacts, including the inevitable pollution with agricultural pesticides, which are ecotoxicants.

Detecting most POPs directly in water is not recommended (Kholubek et al., 2012; Ministry of Health of the USSR, 1987) because many of them are insoluble in water, and soluble POPs can be eliminated through bioaccumulation in living organism tissues. Thus, in our opinion, monitoring surface water for the POP content should begin with bottom sediments. In this case, hydrochemical indicators should be analyzed as the accompanying background or synergistic factor increasing violations in biocenosis and pathomorphology of aquatic organisms (Yemelyanova and Lobchenko, 2002.; WHO, 2011; Kukeyeva et al., 2015; Grancová-Bielková and Sokol, 2010; Akbayeva et al., 2014).

The research aim: Study the content of ecotoxicants in the Akmola region lakes.

In 2016 some of the chemical components was studied in the water and bottom sediments of the Akmola region lakes: Zhalauly and Tastykol lakes, the unnamed lake to the south of the district center of Akkol village and unnamed lake 40 km south from Astrakhanka village, Itemgen lake at Buland village, Zhalanash lake at Malinovka village (near Astana city). These lakes are located on the territory of the agricultural pesticides intensive use or places of POP substances storage. Lakes of the Korgalzhyn lake system: Kokay, Yesey, Sultankeldy are located in the south of the Akmola region territory in the lower part of the Nura River valley, which runs a large farmland. There have also been studied lakes of Shchuchinsk - Borov resort zone Borovoye and Bolshoe Chebachie that are under intensive anthropogenic impact.

In the lakes, hydrochemical samples of water and bottom sediment were selected in the summer months of July - August 2016.

These analyzes have determined the Hydrochemical water pollution index (WPI) (Sibagatullina and Mazurkin, 2009).

Indicators of the MPC excess in the Akmola region lakes for salt ammonium (up to 0.002 MPC), magnesium (up to 1.15 MPC), nitrites (up to 1.12 MPC), petroleum products (up to 1.98 MPC), iron (up to 2.0 MPC ), SSAS (up to 3.8 MPC). High concentration indicators for the sulphate (3.5 MPC), copper (4.3 MPC), magnesium (1.125 MPC). Mainly the lakes are dominated by sulfates, ion chloride (Table 1).

Lakes the most salty and with a hard water are Zhalauly and Zhalanash lakes - the water hardness of 7.5 mg.dm^-3 and 8.37 mg.dm^-3, respectively.

According to the water pollution index (WPI) the first class (relatively clean) may only include Sultankeldy, Yesey, Kokay waters; the second class (slightly dirty) - Zhalauly, Itemgen, Unnamed Lake (Akkol village) Zhalanash, Borovoe, Bolshoe Chebachie; the third class (polluted) - Tastykol, Unnamed Lake (Astrakhanka village) (Sibagatullina and Mazurkin, 2009).

Water is not recommended as a key matrix for lipophilic and non-Arctic initial twelve POPs, so the analysis of surface water is not recommended: for aldrin, chlordane, DDT, dieldrin, endrin, HCB, heptachlor, mirex, PCB, PCDP/PCDF, toxaphene. Water-soluble POPs: chlordecone, α-HCH, β-HCH, γ-HCH, PFOS (perfluorooctanesulfonate). Besides, the POP concentration in water may vary seasonally due to the seasonal activity of phytoplankton and certain organic substances, and other impacting factors, such as rainfall, flow volume, etc. Based on this, we have not detected POPs in the lake waters, and immediately began to define in the bottom sediments, where they can sediment as lipophilic compounds on the adsorbent composed of dead biota, benthic microorganisms.

Almost in all the studied lakes (Table 2), certain POPs have been found, except for the Unnamed Lake (at Astrakhanka village), Borovoye and Sultankeldy. Among the pesticides investigated by us, no sample has such compounds detected as: alpha-hexachlorocyclohexane, beta-hexachlorocyclohexane, chlordecone, hexabromobiphenyl, hexabromodiphenyl ether, lindane, hexachloran, mirex, pentachlorobenzene (in quintozene), perfluorooctane sulfonate and its salts, endosulfan and isomers, tiodan, paraquat. Thus, among 21 tested substances, 12 substances are not accumulated in the bottom sediments of lakes studied.

Lake, where studied chlorinated pesticides are found, are located in areas of the most intensive agriculture, in particular, Zhalauly lake – where 5 pesticides are found (endrin, heptachlor, hexachlorobenzene, DDT, polychlorinated biphenyl), in 3 lakes 3 pesticides are found: Tastykol (aldrin, hexachlorobenzene, DDT), Itemgen (heptachlor, DDT, polychlorinated biphenyl) and Zhalanash (dieldrin, hexachlorobenzene, DDT). One pesticide – (hexa hexachlorobenzene), Bolshoe Chebachie (Aldrin) and Yesey (Aldrin). 2 pesticides were found in Kokay lake (chlordane, hexachlorobenzene).

The quantitative pesticides distribution in lakes is shown in Table 3: aldrin has been found in 3 samples of Tastykol lake (0.06 x 10^-6 mg.kg^-1), Yesey (0.3 x 10^-6 mg.kg^-1), Bolshoe Chebachie (1.8 x 10^-6 mg.kg^-1), chlordane - in 1 Kokay lake (1.3 x 10^-6 mg.kg^-1), dieldrin in 1 Zhalanash lake (0.04 x 10^-6 mg.kg^-1), endrin - in 1 Zhalauly lake (0.6 x 10^-6 mg.kg^-1), heptachlor - in 2 Zhalauly lakes (0.22 x 10^-6 mg.kg^-1) and Itemgen (0.04 x 10^-6 mg.kg^-1), hexachlorobenzene was found in 5 Zhalauly lakes (0.07 x 10^-6 mg.kg^-1), Tastykol (0.47 x 10^-6 mg.kg^-1), unnamed lake in Akkol village (0.066 x 10^-6 mg.kg^-1), Zhalanash (0.5 x 10^-6 mg.kg^-1), Kokay (0.24 x 10^-6 mg.kg^-1), DDT - in 4 Zhalauly lakes (2.3 x 10^-6 mg.kg^-1), Tastykol (1.57 x 10^-6 mg.kg^-1), Itemgen (3.05 x 10^-6 mg.kg^-1), Zhalanash (2.34 x 10^-6 mg.kg^-1), polychlorinated biphenyl - in 2 Zhalauly lakes (0.31 x 10^-6 mg.kg^-1), Itemgen (1.87 x 10^-6 mg.kg^-1). Table 2b

For all studied Akmola region lakes, the POPs content was summed and their specific content identified in the bottom sediments in the region. It is possible to draw up the next POPs decreasing row: 54% (DDT) >12.71% (polychlorinated biphenyl) >12.59% (aldrin) >7.85% (hexachlorobenzene) >7.58% (chlordane) >3.49% (endrin) >1.51% (heptachlor) >0.23% (dieldrin).

The proposed POPs row in the Akmola region may be represented as a diagram (Fig.1).

Thus, the studied waters cannot be classified as toxic as the POPs content in the bottom sediments is of background character, even without exceeding the maximum allowable concentrations of these substances in the water. However, the presence of these substances in the water may indicate the threat growing as environmentally long persistent toxicants will continue to be accumulated by different migration routes, as they are in the water (Gopal et al., 2016). As a result, this can be a serious obstacle to the production of organic products (Kádeková et al., 2017).

The obtained results of the work performed for 2016 allow for the following conclusions:

The MPC excess indicators in the Akmola region lakes are observed for salt ammonium (up to 0.002 MPC), magnesium (up to 1.15 MPC), nitrites (up to 1.12 MPC), petroleum products (up to 1.98 MPC), iron (up to 2.0 MPC), SSAS (up to 3.8 MPC). High concentration indicators for the sulphate (3.5 MPC), copper (4.3 MPC), magnesium (1.125 MPC). Mainly the lakes are dominated by sulfates, ion chloride. Lakes the most salty and with a hard water are Zhalauly and Zhalanash lakes - the water hardness of 7.5 mg.dm^-3 and 8.37 mg.dm^-3, respectively. For the studied water pollution index, the I class (relatively clean) can include Sultankeldy, Esey, Kokay waters; the II class (slightly dirty) - Zhalauly, Borovoye, Bolshoe Chebachie.