Ecological Impacts of Total Petroleum Hydrocarbons

Abstract

Contamination of soil and aquatic ecosystems by petroleum hydrocarbons (PHs) is a serious global issue. The total petroleum hydrocarbons (TPHs) that originate from the distillates of crude oil in the form of diesel, gasoline, lubricating oil, and other typical PHs received much attention globally as contaminants since they are highly toxic, mutagenic, and carcinogenic in nature. Toxicity of PHs increases with increasing molecular weight. Low-molecular-weight cyclic alkanes are more toxic to aquatic organisms than aliphatic and aromatic hydrocarbons of the same molecular weight. In a terrestrial environment, aromatic hydrocarbons are more toxic than aliphatic compounds. Even lower aromatic compounds other than polyaromatic hydrocarbons (PAHs) are toxic. Importantly, the toxicity of PHs in an organism is directly proportional to its bioavailability. Hydrophilic PHs are more bioavailable than the hydrophobic and/or bound PHs. The bioavailable pollutant is highly accessible and adsorbed/absorbed by an organism, causing sublethal or lethal effects by interacting with specific sites/receptors in the organisms. During toxicity development, PHs usually disrupt the cell membrane, which results in the fluctuations in membrane fluidity, integrity, and functioning in the organisms. In aquatic system, non-bioavailable and/or hydrophobic PHs become bioavailable to several benthic organisms (e.g., invertebrates, fish, deposited fish eggs, etc.) as they get adsorbed onto particulates and sediments. Certain aquatic invertebrates (e.g., mussels, oysters, crabs, cockles, etc.) that ingest suspended oil droplets/oil-bound particulates are highly sensitive to PHs. Human beings suffer potential health disorders upon exposure to petroleum compounds via inhalation, ingestion, and dermal contact. An impact in a population that causes no mortality is called sublethal effect, and these effects usually include the development of lesions, developmental defects, changes in molecular functions, and behavioral changes in feeding and breeding. Lethal effects occur in the aquatic environment due to short-term exposure to oil spills, where they disrupt the central nervous system through partitioning into cell membranes and nerve tissues. Fatality caused by PHs is broadly termed as narcosis. In all, the accumulation and persistence of PHs in the environment can bring about harmful effects in both terrestrial and aquatic ecosystems. The present chapter describes several ecological impacts of TPHs on microorganisms, plants, and animals (invertebrates and vertebrates) of both terrestrial and aquatic systems.