Verbundprojekt MICROLAKE - Dynamik von Mikroverunreinigungen und Schwebstoffen mit hoher Affinität im Lake Kinnert und seinem Einzugsgebiet

Abstract

Lake Kinneret, like many other lakes worldwide, is affected by the presence of organic and other pollutants. These contaminants negatively impact water quality in a lake that serves as a unique and sole freshwater reservoir for the State of Israel and the Hashemite Kingdom of Jordan. In addition, such pollutants may induce adverse effects on the organisms inhabiting this aquatic ecosystem. Efficient water treatment of an entire large aquatic body such as this lake (>3.5 × 10⁹ m³) or sediment surface area (~200 km2) are practically unfeasible. In this project we showed that the dominant organic pollutants in this lake are cyclic aromatic petrochemicals identified as mono/poly cyclic aromatic hydrocarbons, namely MAHs and PAHs respectively (disregarding the less toxic aliphatic fraction). The concentration of these compounds, as well as the levels of others (e.g., pesticides) in the water column, is relatively low- mostly <1ppb. Following an intense extraction campaign of "fluffy layer" sediment cores conducted in this study, we showed that the concentration in surface sediments is relatively high and reaches the lower ppm level (though one cannot compare μg/L and μg/Kg). Thus, we consider surface sediments as both a sink and a new potential source of pollutants. Additionally, perimeter dependent spatial- distribution of polluted sediments was noticed, highlighting hotspot perimeters that are thus potentially treatable in various methods. In a similar way, following the use of a custom-made bronze- plastic free corer, extracted microplastics concentrations were assessed in Helgoland. As a result, elevated levels were recorded at specific north-east regions of this lake. In two areas identified in this study, sampled fish population gills and dorsal muscles (edible part) were extracted and analyzed. Consequentially, high levels of specific heavy PAHs e.g., benzo[a]pyrene, benzo[a]anthracene and chrysene, were recorded above the Israeli and the EU thresholds.

To understand the concentration mechanism of polluted sediments in lake specific hot spots, we implied a 3D model, based on particles having either a water density ~1Kg/L or specific densities and settling velocities of Lake Kinneret fluffy sediments sampled, that were analyzed in our lab using a custom-made chamber connected to a LISST-100X device. The 3D model pointed at three areas at the north, northeast and south lake shores, reinforcing our earlier suspicions.

This study also focused on detecting key elements associated with pollutants adsorption potential of each sediment type. To this end, we compared the adsorption levels of deuterated PAHs and MAHs, to selected sediments, with the sediments FTIR spectra (Helgoland) or concentration of specific particles (in the sediment sample) showing specific key densities and sizes. Several high linear correlations are presented. A wholistic model approach is being constructed these days to combine these physical characterizing elements and the pollutants levels. When succeeded, a fingerprint of "sponge like" particles could be followed elsewhere to identify present and future polluted perimeters.

As mentioned above, the revelation that sediment- adsorbed pollutants are focusing on specific hotspots, opens the door to various sediment treatment options. One such potential technique is the use of ozone nano bubbles (NBO3) technology. This method introduces in-situ ozone production to nano scale bubbles. Unlike free ozone or larger bubbles, NBO3 do not evaporate or descend easily from the water column, thus potentially having a long-range oxidation potential. While using a 50L chamber including lake water and 150gr of sediment spiked with deuterated MAHs and PAHs, we were able to show that following only 15 min of mild NBO3 supplying rate, over 90% of the most refractory PAHs were oxidized. These results present the high potential of using this technique in the presence of sediments from this eutrophic lake, having high organic content that did not impair the pollutants' oxidation process. A scaleup of this experiment included the use of a 16m3 pool with 600kg of sediments. A two-day only -activation of the NBO3 system (ozone gas generator integrated into a nanobubbles diffuser), followed by the shutdown of the NBO3 supply, resulted in slow oxidation of the pollutants. Surprisingly, this process lingered days after the shutdown of the NBO3 supply, presenting the low clearance rate of these bubbles and the long-term treatment potential.