Avaliação dos impactos do derramamento de óleo na costa cearense: uma perspectiva baseada nos níveis e fontes de hidrocarbonetos de petróleo e seus riscos ecológicos e alimentares

Abstract

The northeast coast of Brazil has been receiving oil since August 2019 until now, with intermittent sightings of oil off the coast during this period. The main goal of the present work is to evaluate the impacts caused by the oil spill on the inner continental shelf of Fortaleza and on the estuaries of Rio Ceará and Rio Cocó. For this, aliphatic and aromatic hydrocarbons were quantified in surface sediments before and after the event that started in 2019 (sampling years in 2018 and 2020) and also in biota samples (fish, crustaceans and molluscs) from coastal region of Fortaleza city. The species were chosen for their commercial value, their habitat (benthic and pelagic species), and local community preference. They are: oyster (Crassostrea rhizophorae), taioba (Iphigenia brasiliensis), lobster (Panulirus meripurpuratus), red snapper (Lutjanus analis) and Spanish mackerel (Scomberomorus brasiliensis). Regarding surface sediments, the total concentration of n-alkanes (∑n-alc), including pristane and phytane, ranged from 0.8 to 5.4 µg g-1 (mean=2.6±1.2) in 2018 and from 0.4 to 3.4 µg g-1 (mean=2.0±0.9) in 2020. The concentrations of the unresolved complex mixture (UCM) ranged from 36.5 to 51.8 µg g-1 . The profiles of 2020 aliphatic fraction chromatograms do not indicate the presence of oil in most samples not only due to the distribution pattern of n-alkanes but also due to the absence of UCM in most stations. Total concentration of 16 USEPA priority PAHs (Σ16PAHs) in surface sediments ranged from 8.0 ng g-1 to 458.1 ng g-1 in 2018 and from 5.3 to 147.3 ng g-1 in 2020. Surface sediments of Fortaleza inner continental shelf and in the estuary of Cocó River can be classified as slightly polluted and from the estuary of the Ceará River as moderately polluted based on Σ16PAHs. 4-ring PAHs were the most abundant compounds in the sediments from inner shelf and estuaries and diagnostic ratios indicated that the predominant sources of PAHs are pyrolytic both in 2018 and 2020 and there was no change in the origin of PAHs for the sediment in 2020, as expected after the 2019 oil spill. The ecological risk assessment based on the sediment quality index showed that the risk associated with PAH contamination was low in the sediments of Fortaleza inner shelf and Coco River estuary. In Ceará River estuary, the risk associated with sediments was moderate, which may have been affected by the precarious sanitary system around the estuary. In general, the potential risk of environmental exposure to PAHs calculated based on the carcinogenic potencies relative to BaP for surface sediment samples off the coast of Fortaleza is low for human health. Regarding biota, data obtained indicate that the organisms sampled, in general, contain low concentration values of PAH in muscles of fish, crustaceans and taioba, reflecting low bioaccumulation of PAHs by these organisms in the studied region, which does not represent a significant risk to human health through consumption. However, oyster consumption presents a risk to human health, mainly due to the contribution of BaA and Cri, which are PAHs characteristically related to pyrolytic activities and were found in high concentrations in this species in Cocó River estuary. The PAH bioaccumulation data for fish, mollusc and crustacean species of this study can serve as a reference for future works evaluating the impact of this oil spill, since the consequences of this event are expected to persist in the environment for long periods, as observed in other oil spill accidents around the world.