Growth stimulation effects of environmentally realistic contaminant mixtures on a marine diatom

In this research we investigated whether or not marine algae growth was affected when exposed to environmentally realistic mixtures of chemicals collected from the Belgian part of the North Sea (BPNS). To explore this, we used a specific sampling technique that “filters” chemicals from the seawater and collects them in a way allowing to transfer these mixtures from the field to the laboratory. Once brought to the lab, we determined the concentration levels of 88 personal care products, pesticides and pharmaceuticals. Next, we exposed marine algae to the so collected mixtures of chemicals and recorded the algae’s growth over three days. We repeated these tests 3 times within 16 months and surprisingly observed growth stimulation for those mixtures with less sample handling and short storage while those undergoing repeated handling and longer storage showed no effects. In an explorative try to define the differences in the mixture composition of the effect- and no-effect causing samples, we were indeed able to define these differences but our findings could not be linked to the biological effects observed. In conclusion, we have shown that environmentally realistic mixtures of contaminants collected in the BPNS can enhance the growth of a marine algae species but it remains challenging to define those substances within these mixtures that actually cause effects on algae growth.

Scientific abstract

In order to estimate mixture effects caused by the high number of chemicals simultaneously present in the environment, methods for routine effect assessment of environmentally realistic contaminant mixtures (ERCMs) are needed. Here, we repeatedly exposed the marine diatom Phaeodactylum tricornutum to SpeediskTM passive sampler extracts and observed statistically significant growth stimulation up to 6 % and 7 % for samples from inside and outside the harbor of Zeebrugge, respectively. These effects were found at summed contaminant concentrations (159 – 166 ng L‐1) that were within a 1.1‐ to 2.4‐fold range of those observed in grab water samples taken during sampler deployment. These stimulatory effects were confirmed in two independent tests with extracts stored for <1 or 8 months and that had undergone limited sample handling, while no effects were observed for extracts that had been stored for 16 months and had undergone repeated handling (notably repeated freezing and thawing) before biotest spiking. Targeted analysis by UHPLC‐HRMS was performed to quantify 88 personal care products (n = 8), pesticides (n = 28) and pharmaceuticals (n = 52). Among these compounds, multivariate statistical analysis put forward the β‐blocker atenolol as explaining most of the observed variation in mixture composition between the growth stimulating and no‐effect causing extracts. However, when tested individually over the entire concentration range present in the extracts, atenolol did not have any effect on P. tricornutum suggesting that non‐targeted substances in the extracts may have contributed to the observed stimulatory effects. Nevertheless, our study shows that exposure to contaminant mixtures at environmentally realistic concentrations can lead to small but significant growth stimulation effects on the marine diatom P. tricornutum.

Full reference (link):

Moeris, S., Vanryckeghem, F., Demeestere, K., Huysman, S., Vanhaecke, L., & De Schamphelaere, K. (2019). Growth stimulation effects of environmentally realistic contaminant mixtures on a marine diatom. Environmental Toxicology and Chemistry.