Phthalate contamination in agricultural and non-agricultural soils around landfills in Guilan Province, Iran

There are growing concerns about the negative impact of soil and forest pollution from improper waste disposal and leachate production on soil and ecosystem quality. Favorable climate and rich soils have made Guilan Province one of Iran's major agricultural centers. Phthalates (PAEs), also known as phthalic acid esters (PAEs), are common plasticizers that may pose a ubiquitous risk to the environment because they are difficult to degrade. This study investigated the environmental impact of PAEs at 26 sites in 5 cities in western and central Guilan Province. For this purpose, a total of 4 to 7 mixed soil samples were collected from both agricultural and non-agricultural lands, at a distance of 100 to 700 meters from each landfill in all directions. The physicochemical parameters of the soil samples, including moisture content (MC), pH, electrical conductivity (EC), total organic matter (TOM), and PAEs, were then measured. The PAE concentration was measured using the standard extraction method (EPA Method 8061 A) in a gas chromatography - mass spectrometry (GC - MS) instrument. The results of the study showed that the concentration of PAEs in agricultural and non-agricultural soils was significantly different (p < 0.05). The highest concentration was related to BEHP with 59.6% (14.37 ppb in agricultural soils and 50.61 ppb in non-agricultural soils). Other PAEs identified included DOP at 26.99% (10.54 ppb in agricultural soils and 20.89 ppb in non-agricultural soils), DMP at 11.48% (7.61 ppb in agricultural soils and 7.33 ppb in non-agricultural soils), IBP at 1.69% (0.67 ppb in agricultural soils and 1.31 ppb in non-agricultural soils), DEP at 0.09% (0.03 ppb in agricultural soils and 0.07 ppb in non-agricultural soils), BBP at 0.14% (0.04 ppb in agricultural soils and 0.11 ppb in non-agricultural soils), and DBP at 0.1% (ND in agricultural soils and 0.01 ppb in non-agricultural soils). The mean PAEs concentration in non-agricultural areas was significantly higher than in agricultural areas (p < 0.05). The results also indicated that the highest PAE concentration was in Talesh (13.57 ppb, 29.52%), followed by Anzali (10.71 ppb, 23.31%), Astara (8.91 ppb, 19.38%), Saravan (8.78 ppb, 19.10%), and Astana (4 ppb, 8.70%), respectively. The risk assessment results in our study indicate that the levels of PAEs, especially BEHP and DNOP, are significantly higher than the standards set by the MRL, TDI and RfD. Specifically, BEHP values in agricultural and non-agricultural settings were reported to be 14.17 and 50.41 times higher than the RfD and MRL, respectively. DNOP values in agricultural and non-agricultural settings were also 3.54 and 20.49 times higher than the MRL and TDI, respectively. While DBP values in non-agricultural settings were 0.01 ppb lower than the MRL (0.5), they still pose a serious acute and chronic risk. The results of this study emphasize the need for proper waste management and continuous monitoring of soil quality to prevent the negative effects of these pollutants on the environment.Implications: This study addresses growing concerns about soil and forest pollution caused by improper waste disposal and leachate in Guilan Province, a key agricultural region in Iran. By analyzing the concentration of phthalates (PAEs) - persistent plasticizers harmful to the environment - in soils from 26 sites across five cities, we provide critical data on contamination levels in both agricultural and non-agricultural lands. Our findings highlight significant differences in PAE distribution, with notably higher concentrations in non-agricultural soils, and identify key PAE compounds affecting soil quality. These results are essential for environmental managers and policymakers to develop targeted strategies for soil protection and pollution mitigation in Guilan and similar agricultural regions.