Assessment of pollution with heavy metals and petroleum products in the sediments of Varna Lake

Abstract

We present the results from the first large-scale study on pollution in the Varna Lake sediments, which was implemented in two preselected zones with significant importance for developing economic activities and urban planning. Based on 140 probes, we developed a digital map of the pollution gradients in these zones. The sediment analysis shows that the pollution levels at specific locations significantly exceed the international standards for contamination with heavy metals and petroleum products. The reported pollution concentrations can be linked to various contamination sources, such as rivers, ports, the chemical industry, and WWTPs (Waste water treatment plants), located on the shores of the lake. The high values of pollution with iron, copper, and petroleum product registered in the sediments of Lake Varna indicate the need for sustainable management of human activities in the area. The presented findings motivate urgent measures for cleaning and improving the ecological situation in Varna Lake, which is an integral part of the ecosystem of the city of Varna and other municipalities bordering the lake. The results of the study indicate that urgent action is needed to address the high risks associated with the observed sediment contamination.

Pollution of Varna Lake and possibilities of using the pollutants as resources

“…After an analysis of the average contamination of all samples from the two areas of interest, it was observed that the most significant accumulation of iron, lead and copper is in Zone 1, and the highest pollution in Zone 2 is due to arsenic, mercury and petroleum products Figure 2. The accumulation of these heavy metals and petroleum products in the sediments of Varna Lake is due to the solid industrial pressure, urbanisation and shipping [3]. After a comparison of the average values of pollution in the two zones, it was observed that the indicators -mercury, copper and petroleum products prevail over the others.…”

“…Another reason for the difference in the contamination could be that in Channel 1, periodic dredging of the bottom is carried out to provide a navigable depth Figures 3 and 4. Given the direction of movement of the lake waters and the location of the dredged material dump, there is a possibility that fine sediments and their pollutants are transported to the Old Channel [3]. All accumulated pollutants in the sediments of Varna Lake are continuously released into the water body and contribute to maintaining its poor ecological condition.…”

“…Each sample was taken 40 cm below the bottom level. Sampling was carried out by qualified diving teams in two pre-selected target areas (Zone 1 and Zone 2), according to a predetermined measurement grid with a distance between sampling sites of 200 m [3]. Zone 1 covers the eastern parts of Varna Lake and the two navigation channels connecting it to Varna Bay.…”

“…for petroleum products but are broken down by type. Therefore, when preparing the legend for petroleum products, the reference value was taken based on the average value of the laboratory samples, and the rest were defined as contaminated and uncontaminated areas [3].…”