Potential environmental risk assessment of di-2-ethylhexyl phthalate emissions from a municipal solid waste landfill leachate

Characteristics of sampling sites and location

A quarter of the municipal solid waste (MSW) landfill “MZO Pruszków” was chosen for this research. Permission to obtain samples was granted by the landfill management on 11.12.2013. The landfill has been used for the disposal of non-hazardous and inert waste from neighbouring towns and the capitol city Warsaw, but there is no precise record of its contents. The landfill opened in 1965 and is located in Mazowieckie Voivodship, near Pruszków city, 20 km from the center of Warsaw, the capital of Poland (52°10′40.0″N 20°46′34.4″E) (Fig. 1). The investigated quarter of the landfill was opened in 2007, it has synthetic bottom isolation, and systems for controlling and collecting leachate in a temporary 48 m³ roofed storage tank. The 35 m high quarter, which is currently under a closing process, occupies around 1 ha and contains nearly 447000 m³ of waste. The leachate is transported to a local STP located 2 km away from the landfill.

Sampling and quality control/quality assurance

Leachate samples were collected three times per year over three years from 2014 to 2016 from the landfill. Sampling took place in each of the four “meteorological seasons” to examine seasonal variation on ambient temperature, precipitation, evaporation and water content in the waste, which could affect DEHP concentrations.

Irish EPA guidelines (Cambell et al., 2003) were used during the collection of three separate samples of raw leachate. Whenever possible, individual samples were taken at different locations and depths across and within the raw leachate tanks.

In 2015 and 2016 two piezometers installed by the landfill managers upstream and downstream of an aquifer near the landfill for monitoring purposes were used to collect groundwater samples. Water samples from the piezometers were collected using a submersible pump with a maximum capacity of 9 L/min. Water was collected after cleaning the piezometers by pumping out stagnant water in the borehole several times or after pumping out water from the borehole for a specified time. Guidelines for groundwater sampling in accordance with PN-EN ISO 5667-11:2004 were followed.

All samples were collected using a stainless steel bucket, Teflon tubes and clean glass jars. A portion test material was poured to the top of the jars to eliminate oxygen contact during transportation. After collection, the samples were immediately sent to the laboratory for chemical analysis. No plastic materials were used during sampling, transportation or analysis to avoid contamination. Glass jars and aluminium foil (used for insulation under the jar’s cap) were first washed with water and detergent solution then rinsed several times with distilled and Milli-Q water and dried for several hours in a 200 °C oven. All jars were also rinsed with water or leachate before sample collection.

Overall there were 26 leachate and 19 water samples collected and analysed in the study. The collected leachates were yellowish brown to dark brown in color. Table 2 presents weather details and seasons of sampling.

Instrumental analysis

The first three series of leachate samples in 2014 (summer, autumn and winter) were analysed using GC–ECD methodology and all the subsequent series in 2015 and 2016 were analysed using GC-MS methodology described below. The main reason for the change was that GC-MS methodology was accredited and it was acknowledged that international accreditation would ensure the highest quality of analytical results. Details about each methodology can be found in the references cited and in the supplementary materials (Supplemental Data S1).

EUSES modelling

During our modelling using EUSES program default data from the defined standard environment, main DEHP characteristics such as physicochemical properties (source: Pakalin et al., 2008) and local specific data (obtained DEHP concentrations and emissions, local measured temperatures and precipitations) were used to calculate the predicted PEC environmental concentrations on a local scale.

For a multitude of environmental compartments including freshwater bodies and sediments, STP sludge, soil, and for secondary poisoning, the endpoints and PNEC values have been developed at the European level and published in the ECHA report (ECHA database, 2021) and the DEHP European Union Risk Assessment Report (EU RAR) (Pakalin et al., 2008). According to the report no long term studies indicating effects on aquatic organisms exposed to DEHP existed at the time of EU RAR (Pakalin et al., 2008), therefore PNEC_water  could not be specified. However, the results of a 2013 long-term study of the apparent water solubility of DEHP were deemed acceptable, in which DEHP concentrations of 0.2 g/L impaired reproduction in zebra fish (Danio rerio): thus the PNEC_water was determined to be 0.07 g/L (Corradetti et al., 2013). This test, as well as the PNEC_water, were also found to be reliable and were therefore used in the PAE risk assessment performed by the Government of Canada in 2017 (Environment and Climate Change Canada, 2017). All collected endpoint and PNEC values are summarized and presented in Table 3.

The outcomes of EUSES modelling were PEC and RQ values.

If RQ (PEC/PNEC) < 1, the substance is not considered of concern and no unacceptable risk to the environment is identified. However, if the RQ ratio > 1, a potentially unacceptable risk is identified and further testing and risk reduction measures should be considered (Gruszecka & Helios-Rybicka, 2009).

DEHP concentrations in groundwater and landfill leachate

In groundwater, in 2015 and 2016 all samples upstream and downstream piezometer’s water resulted in DEHP concentrations below LOQ, except for one sample in autumn 2016 of 1.5 g/L (Table 4).

The results of DEHP concentrations in raw leachate are presented in Table 4 and Fig. 2. DEHP was detected in 88.5% of leachate samples from the landfill (24 out of 27 cases).

The average concentration in each year (Table 4) was calculated using highest observed DEHP concentrations from each sampling season while assuming a worst-case scenario (WCS) for further calculation. The highest average concentration was in 2014 at 200.4 µg/L; 2015′s highest average concentration was 61.5 µg/L; and 2016 had the lowest value at 23.3 µg/L.

Seasonal changes

Average seasonal precipitation was calculated based on data from the nearest weather station in Pruszków. From these data annual precipitation were calculated (for more details please refer to Table 4). The highest sums of annual precipitation of 667.6 mm were observed in 2016; the lowest in 2015 of 407.6 mm; while 2014 held a value of 622.4 mm.

Risk assessment

For the purpose of modelling, the predicted main routes of DEHP emissions in leachates from Mazowieckie Voivodeship municipal landfills to the environment and an estimated percentage of total DEHP amounts were developed by the authors and are presented in Fig. 3. The storage of sewage sludge on the STP premises is assumed to be a temporary condition, WCS was assumed in the risk analysis of sewage sludge agricultural applications. Considering the information presented in Fig. 3, it may be assumed that from municipal landfills without bottom sealing and a leachate collection system, 100% of the DEHP load in leachate will make its way to the environment. In contrast, for municipal landfills with bottom sealing and leachate collection, 6.8% of the DEHP phthalate load could be released directly to the environment from municipal wastewater treatment plants; 11% of the load is dumped into the environment as a result of sewage sludge storage and 4.6% is transferred to the environment as a result of legal agricultural use of sewage sludge. Based on our calculations 22.4% of the total DEHP load was destined for additional analyses and EUSES modeling.

Possible routes of DEHP emissions in leachate from municipal landfills (with and without bottom sealing) into the environment were analysed and a risk assessment algorithm was developed by the authors (Fig. 4).

Using EUSES modelling PEC values (for the sewage sludge application of 3 and 15 Mg/ha/year) and RCR values were calculated and are presented in Tables 5 and 6 respectively. RCR >1 for the local fresh-water compartment (RCR of 16.1) and for worm-eating birds and mammals (RCR of 8.63) for a maximum sewage sludge application in agriculture of 3 Mg/ha/year. RCR of 43.2 was obtained for worm-eating birds and mammals for a maximum sewage sludge application for other purposes, such as: reclamation of land for non-agricultural purposes; cultivation of plants intended for compost production; and cultivation of plants not intended for consumption or production of fodder (15 Mg/ha/year).

The results of this study indicated RCR values below 1 for compartments including local fresh-water sediment, local soil and microorganisms of a sewage treatment plant, and fish-eating birds and mammals (fresh-water).

For more information please refer to the full EUSES Reports included in Supplemental Data S2 and Supplemental Data S3.

DEHP concentrations in groundwater and landfill leachate

Our results suggests no DEHP contamination of groundwater, which means the landfill’s synthetic bottom isolation, and systems for controlling and collecting leachate, continues to work properly.

The most recent study on leachates from active and closed landfills in Poland (Kotowska, Kapelewska & Sawczuk, 2020), also reported similar DEHP concentrations in the range of LOQ - 249 g/L and LOQ - 143 g/L respectively, but other Polish researchers (Fudala-Ksiazek, Pierpaoli & Luczkiewicz, 2017) reported much higher DEHP concentrations: 8201 g/L. The variability of these results suggests that DEHP concentrations in MSW landfills’ leachate can be large. Many reasons may account for such difference, such as local precipitation, ambient temperature and water content in the waste, sampling season, landfill age and design (including the methods of compacting, top cover and type of surface vegetation), capture and storage of leachate (open or close tanks) and the related surface runoff and dilution of leachate; therefore concentrations may differ across countries as well as individual landfills (Kotowska, Kapelewska & Sawczuk, 2020; Marttinen, Kettunen & Rintala, 2003a; Renou et al., 2008). The range of raw leachate DEHP concentrations in this study are similar to those found in the scientific literature (Table 1), where concentrations ranged from “not detected” to 460 g/L. The level of DEHP in the leachate in our study was similar to those reported in China (Feng et al., 2018), Puerto Rico, Germany, Sweden (Zolfaghari et al., 2014) and Canada (Horn et al., 2004). Our analyses showed DEHP concentrations much higher than those reported on two landfills in China (Liu et al., 2010; He et al., 2015), eleven landfills in Sweden (Kalmykova et al., 2014; Jonsson et al., 2003) and six landfills in Denmark (Jonsson et al., 2003). The difference in DEHP concentrations could be also attributed to the composition of landfilled waste, mainly the amounts and types of plasticizers used in Asia, Western and Eastern Europe.

Such variability indicates the need for more research to understand the multifactorial effects DEHP concentrations in leachate.

Seasonal changes

The highest measured DEHP concentrations in each year occurred during the lowest average seasonal precipitation: 394.4 g/L in autumn of 2014 with 16 mm, 73.9 g/L in the summer of 2015 with 33 mm, and 31.1 g/L in the spring of 2016 with 30 mm of precipitation.

It should be noted that 2015 was a year with a small amount of precipitation and prolonged drought during the summer, which might have affected measured DEHP concentrations.

In WCS of DEHP concentrations, only a seasonal correlation (−0.62) between concentrations and mean precipitation was found. Other places where the seasonality is observed have found no seasonal correlation related to DEHP concentrations; which may suggest landfill design and operations can prevent the effect of the seasonal changes. In the study by Asakura, Matsuto & Tanaka (2004) no seasonal or annual dependence of DEHP concentrations in leachate from landfills in Japan was observed.

Risk assessment

The developed algorithm of risk analysis related to phthalate emission in leachate from municipal landfills (Fig. 4) in EUSES is a widely-available tool for forecasting exposure to environmental elements at particular stages and can also be adopted for other contaminants in leachate from municipal landfills.

In our study, all leachate was collected and transported to the local municipal STP, and therefore ERA was carried out for DEHP in the leachate at the STP.

Our results indicated no risk for microorganisms of sewage treatment plants, along the conclusions of the EU RAR (Pakalin et al., 2008).

Obtained unacceptable potential risk for the local fresh-water compartment and for worm-eating birds and mammals (for sewage sludge applications) indicate the need to take risk reduction measures. Also the EU RAR (Pakalin et al., 2008) concluded that there is a need for limiting the risk posed by DEHP emissions to aquatic and terrestrial ecosystems (for sites processing polymers with DEHP or sites producing printing inks, sealants and/or adhesives with DEHP) and that there is a need for further information and/or testing.

In a recent study by Kotowska, Kapelewska & Sawczuk (2020) risk quotient values were calculated for DEHP with respect to effluent wastewater. Their results indicate that DEHP poses a high environmental risk for all trophic levels (algae and cyanobacteria, invertebrates, and fish) in effluent wastewaters considered in the study. The study also concluded that further action is needed to reduce the contamination of water with phthalates from landfills and sewage treatment plants.

As DEHP is trapped on sludge, due to its high log Kow (Tran et al., 2015), high concentrations may be present in treated sludge destined for agricultural use (Marttinen et al., 2003b). The Danish Veterinary and Food Administration reports that DEHP is not degraded in STP but mainly distributed to the sludge (Ladefoged, Nielsen & Muller, 2004). DEHP accumulation in sludge may restrict its agricultural usage (Marttinen, Kettunen & Rintala, 2003a): the maximum acceptable value of 100 µg/g d.w. for sludge to be used in agriculture proposed by the European Commission (Marttinen et al., 2003b) is not incorporated into Polish sludge regulations. If sludge is uncontrolled (both in terms of the amount of applied doses and the preparation of the sludge prior to use), risks to the soil and groundwater from DEHP pollution remains high. In that context, the monitoring of DEHP in sludge and agricultural soil may contribute to improvements in the regulation (inter alia in Poland) recommending maximum levels of DEHP contaminants in sludge for agricultural application.