Toxicity of Naphthenic Acids on the Chlorophyll Fluorescence Parameters and Antioxidant Enzyme Activity of Heterosigma akashiwo.

Huanxin Zhang,Qiang Kong,Zhihao Lin,Wenlong Dong,Yumiao Zhou

doi:10.3390/antiox10101582

Abstract

Petroleum hydrocarbons can serve as a carbon source for marine phytoplankton; so, marine high-acid crude oil pollution events are likely to result in algal outbreaks or harmful algal blooms (HABs) in surface waters. Naphthenic acids (NAs) are the primary acidic component of crude oil, and red tide is of great concern due to its high diffusivity and strong destructive properties. It is important to study the mechanism of the toxic effect of NAs on the typical red tide algae, Heterosigma akashiwo, for the balance and stability of marine algae. The mechanism of NAs’ damage effect was investigated in terms of the antioxidant enzyme activity, cell number, the chlorophyll positive fluorescence parameters, and the cell morphology of microalgae. Experiments confirmed the hormesis of low-concentration (0.5, 2, and 4 mg/L) NAs on Heterosigma akashiwo, and the indicators of high-concentration (8 and 16 mg/L) NA exposures showed inhibition. In this study, the toxic effect of NAs on the target organism showed a clear concentration–dose relationship. The 16 mg/L NAs stress caused severe damage to the morphology and structure of the target biological cells in a short time (96 h), and the population growth decreased. The target organisms showed a staged oxidative stress response to NAs. The behavior in the low-concentration treatment groups showed toxicant excitatory effects on the photosynthetic efficiency and antioxidant enzyme activity of the target organisms. This study provides theoretical and practical data for the development of an important toxicological model of the toxicant’s excitement effects and antioxidant defense mechanisms. In addition, it provides prospective research data for the prediction and avoidance of ecological risk from NA pollution in marine environments.

Highlights

The frequent occurrence of oil spills in coastal areas makes marine crude oil pollution an important environmental problem [1]
Petroleum spills have resulted in large amounts of Naphthenic acids (NAs) entering the environment, and they are being found in environmental media such as groundwater, rivers, lakes, and sediments
The results of this study showed that NAs have a significant effect on the photosynthesis of H. akashiwo, and its effect on photosynthesis was closely related to its concentration

Summary

Introduction

The frequent occurrence of oil spills in coastal areas makes marine crude oil pollution an important environmental problem [1]. According to the current domestic demand, the use of high-acid crude oil is increasing. The current production of high-acid crude oil accounts for approximately 5% of the total global crude oil production each year and is increasing at an annual rate of 0.3% on average [2]. Naphthenic acids (NAs) are the primary acid component in high-acid crude oil, and its weight ratio in crude oil is 1–2% [3,4]. Petroleum spills have resulted in large amounts of NAs entering the environment, and they are being found in environmental media such as groundwater, rivers, lakes, and sediments. The compounds have been detected in aquatic organisms, such as freshwater fish [5,6,7,8]

Methods

Results

Discussion

Conclusion