Collecting and disposing of urban wastes due to population growth and industrialization, and consequently the increase of waste generation per capita, has become one of the most important issues of municipal waste integrated management 1, 2. It is clear that Iranian municipal waste management system is in a relatively critical situation 3, 4. This gets more complicated when its negative and harmful effects are examined in relation to other existing systems, including the environmental system 5, 6. One of the main problems of landfills is waste leachate. Waste leachate is a kind of wastewater with high concentrations of organic and mineral compounds, and sometimes contains a high level of toxic pollutants such as arsenic, lead, cadmium, and chlorinated organic compounds 7-10. Many parameters affect the quality and quantity of leachate, such as climate, landfill and compression methods, buried waste composition, landfill structure, and the type of soil in the area 11-13. The main risk of leachate from landfill is its infiltration into groundwater or mixing with surface water and soil pollution. In addition, numerous animal and plant species around aquifers that are polluted by contacting with leachate are severely exposed to pollution which ultimately will have adverse effects on humans themselves 14-16. Limited activities have been carried out in Iran regarding leachate control. Due to population growth and industries development, the amount of waste produced has also increased and, as well as the number of landfill sites, and large amounts of leachate discharged into the environment. This issue has increased environmental and health risks 17-19. The study of landfill site and leachate pollutants is one of the requirements of urban communities to avoid leachate risks and other environmental problems.

Parvaresh et al. studied the concentration of heavy metals in urban waste leachate and their removal methods. According to the results of the study, the concentration of elements studied in the leachate far exceeded the standards of the US Environmental Protection Agency (EPA). The use of coagulant alum can eliminate the concentration of heavy metals in waste leachate with considerable efficiency 20. Shokouh et al. studied the quality of leachate from urban landfills and the compost plant in Mashhad. In this study, the amount of leachate pollutants in winter and spring was measured. The results showed that the produced leachate had much more organic material than other landfills in other countries 21. Haji Nejad et al. conducted a study on the effects of landfill leachates on the quality of groundwater in Bojnourd. They sampled two upstream wells and two downstream wells at landfill site and measured the parameters NH3, NO3-, PO43-, SO42-, Mg2+, Cl-, K+ و N+. Their results showed that the concentration of most pollutants was higher than standard, causing the release of leachate from landfill to groundwater and contamination of adjacent wells 22. Salem et al. conducted a study in Algeria to analyze the contamination of Landfill leachate. The area studied was on the site (Ouled Fayet) West of Algeria, which has been active over the past 5 years, and has received non-hazardous, urban and assimilated wastes from 34 municipal districts with 363,000 tons of waste per year. Several samples have been taken at Landfill entrance and exit locations. The results showed that the leachate contains organic materials and a high level of biodegradable materials; furthermore, it was stated that longer durability did not reduce the level of the parameters. A chemical deposition approach was also proposed to prevent the effects of heavy metals pollution in future 23. Melnyk et al. examined the chemical pollution and toxicity of leachate samples resulted from urban solid waste in Bangladesh in 2007-2011. Sampling was carried out in two stages. In the first stage, the sample was taken before entering water to the landfill, and in the second stage the sample was taken at the outlet of the water stream at the landfill site. The pollution resulted from toxicity in 2007 to 2012 was much higher than the samples taken in 2010- 2012 24. Munir et al. examined leachate and leachate pollution index at landfill site in Lahore, Pakistan. They analyzed the characteristics of leachate and calculated its pollution potential by leachate pollution index (LPI) at two landfills sites. The pH value in one site was alkaline, and in another was acidic, all three landfill sites had very low dissolved oxygen. In all three landfills, pH, BOD5, COD, PO43-, NO3-, Cl- in winter and summer were significantly higher than the standards of Environmental Protection Agency (EPA) in the U.S 25. De et al. in Kolkata, India, examined leachate and dominant pollutants using leachate pollution index for uncontrolled landfill sites. The results of physicochemical and biological analysis of leachate showed that the analyzed parameters of TDS, BOD5 COD, TKN, NH3-N, Cl-, Pb و Hg in all landfill sites ,were higher than the standard leachate discharge for surface waters set by principles of 2013 solid urban waste. In addition, total concentrations of Cr and Zn are higher than the leachate release standard for landfill sites. In terms of contamination rating, total bacterial coliform, TKN, NH3-N and Hg were identified as dominant pollutants and the most important contributing factors in leachate pollution index 26.

Considering the necessity of evaluating the landfill site in Tonekabon, due to its slope towards the river (Do Hezar and Se Hezar), eventually these surface waters reach Caspian Sea; furthermore, high humidity and high rainfall and high level of underground water in the region have become a research priority for respective organizations and have been of particular importance. The present study was conducted to investigate the status of landfill-borne pollutions at landfill site in Tonekabon. It was conducted to make authorities aware of the situation in the region in order to have a proper management despite time, place, and financial constraints in a one-year period.

Area of study

Tonekabon is located in west of Mazandaran province. The city is bounded to Caspian Sea from north, from south to Alborz Mountains, from the center to Qazvin province, from east to Chalous, and from west to Ramsar city. The city consists of four districts (Markazi, Khorramabad, Abbasabad and Nashta), nine villages and cities of Tonekabon, Abbasabad, Nashtarood, Clarabad, Khoramabad and Salman Shahr. The northern part of Tonekabon is a plain in which there are urban areas and most of villages.

Regarding the climate and based on the information from climatology station in Khoshkedaran, Tonekabon has a very humid climate, which holds truer about northern areas of the city and southern areas of the city have somewhat cold and mountainous weather. The average annual rainfall is 1131 mm. The studied landfill is in Pardehsar, a suburb of Khorramabad in Tonekabon which is located on Do Hezar road, with latitude of 36 degrees, 41 minutes and 54 seconds, and a longitude of 50 degrees, 49 minutes and 12 seconds. The selected area for the study is 500 meters above the sea level and the surrounding area is quite forested and pluvial (Figure 1). The slope of the landfill site from the south is towards the north and field slop is about 45%, with 8 hectares of land. The distance from the village is about 500 meters and from Tonekabon, it is 12 kilometers. The major rivers of the area include the rivers of Do Hezar and Se Hezar, and local streams. The soil of the region is generally clayey which reduces the penetration rate of leachate into groundwater. At this landfill site, municipal waste is collected from Tonekabon and is buried (Interview with Tonekabon Municipality experts). According to the authorities in Mazandaran province, 3,100 tons of waste is produced per day, 75 percent of which are wet wastes.

The qualitative parameters measured in all the chapters under study include BOD5, COD, TSS, TDS, pH, EC, the results of which are given in the following. In order to investigate the level of leachate penetration into surface waters, four samples were studied, as shown in Fig. 1. The first sample is taken from the end of the site where the waste is disposed of and leachate is flowed. (station 1), the second sample is from about 450 meters downstream the landfill (station 2), the third sample is from a 600 meters distance (station 3) and the fourth was sampled at a distance of 1700 meters, where the surface water containing leachate interferes with Do Hezar river (station 4). It should be noted that sampling time interval was set to be during a year and in four periods from the summer of 1916 to the spring of 1917, with each season being sampled in four specific places. Table 1 shows the results of the measurement average at sampling stations in four seasons and at four stations.

Due to the normality of the variable data include (TDS, PH, TSS, EC, BOD5 and COD) One-way ANOVA and Duncan's tests have been used.

As the results of Duncan's test (Table 4) for quadruple stations show, the average values ​​of pH for sampling stations are in the same group, which means that the mean of all stations is in the same group. In the EC parameter, the stations studied are classified into three groups: the first group-the third and fourth stations; the second group - the second station; the third group-the first station. 

BOD5: According to Table 4, the investigated stations are classified into three groups: the first group-the third and fourth stations; and the second group-the second station; the third group-the first station