The impact of cement factory fumes and car exhaust on the presence of lichens in the city of Leptis

This study focused on identifying the extent to which lichens are affected by air pollutants such as sulfur and nitrogen oxides. Therefore, this study focused on surveying and identifying the most important lichens in the local environment, and thus the possibility of using them as an indicator of air pollution resulting from vehicle fuel combustion due to transportation, fossil fuel combustion at the desalination plant, smoke from cement factories (Labdah-Al-Marqab), and ship traffic in the port. Lichens are considered among the best examples of symbiosis and interdependence in the plant kingdom, and they play a prominent role in soil stabilization and rock formation. Their importance has emerged since the last century as a vital indicator of air pollution in areas near factories and transportation due to the lichen's ability to store heavy materials, such as sulfur and nitrogen oxides. A number of lichen samples were collected and classified according to classification keys. At least four species were found to be dominant in the region, including crustacean lichens such as Lecidea and foliose lichens such as Xanthoria. The city of Lebdah is affected by surrounding pollution sources, such as its proximity to the coastal and secondary roads, the cement factories in the region, and its proximity to... Power plant.

Therefore, the ancient city is affected by these sources and contains high concentrations of pollutants. Lichens are used as effective bioindicators of changes in the atmospheric content of various substances, given their sensitivity and rapid absorption of these various substances. Numerous studies have shown a correlation between the concentration of various elements in the lichen body and the content of these elements in the surrounding air, as well as the lichens' distance from pollution sources.

Lichens are perennial organisms, which makes them vulnerable to pollution for long periods of their lifespan. Their moisture content (poikilohydric) varies depending on the nature of the surrounding air and its moisture content. Suspended substances in the air, whether dry or wet (aerosols), settle on the lichen body, which absorbs these substances. Some lichens can also absorb additional elements from the environment in which they grow, such as rocks and soil. Given these characteristics, lichens are sensitive to disturbances caused by human activity that pollute the environment. Long-term lichens in a given area can be relied upon to identify the local environmental conditions they experienced, providing a long-term reflection of these conditions.

Lichens fully or partially rely on passive ion exchange to absorb elements from their environment. This means that the lichen body absorbs the nutrients it needs for growth, as well as other elements that are not essential for growth and may even be harmful and lethal, such as heavy metal cations (Dillman, 1996).

In general, there is a significant positive correlation between air pollution levels in a given area and the resulting damage to lichen cells and tissues, especially under humid conditions. In dry areas, lichen bodies rehydrate for shorter periods compared to humid areas, resulting in moisture stress that interferes with air pollution from harmful elements. This accelerates cell damage and tissue death in lichens, especially in sensitive species. Samples are usually collected from lichen populations in the wild, dried, ground, and chemically analyzed to identify the elements accumulated within their bodies. The results are compared with other lichen samples growing in contaminated areas (Cabrall, 2003; Chettri et al., 1998; Branquinho et al., 1997).