# Natural sea water and artificial sea water are not equivalent in plastic leachate contamination studies

## TL;DR

Natural and artificial seawater produce different plastic leachate compositions, affecting toxicological studies and marine life development.

## Contribution

Demonstrates that natural and artificial seawater are not equivalent for plastic leachate studies, impacting toxicological conclusions.

## Key findings

- Zinc leaching from PVC plastic is reduced up to five times in artificial seawater compared to natural seawater.
- Leachates from different seawater types cause varying developmental effects in the tunicate Ciona intestinalis.
- Not all artificial seawaters are suitable for studying marine organism development.

## Abstract

Plastic contamination is one of the concerns of our age. With more than 150 million tons of plastic floating in the oceans, and a further 8 million tons arriving to the water each year, in recent times the scientific community has been studying the effects these plastics have on sea life both in the field and with experimental approaches. Laboratory based studies have been using both natural sea water and artificial sea water for testing various aspects of plastic contamination, including the study of chemicals leached from the plastic particles to the water.

We obtained leachates of PVC plastic pre-production nurdles both in natural and artificial sea water, and determined the elements in excess from untreated water by Inductively coupled plasma – optical emission spectrometry. We then used these different leachates to assess developmental success in the tunicate
Ciona intestinalis by treating fertilised eggs through their development to hatched larvae.

Here we report that chemical analysis of PVC plastic pre-production pellet leachates shows a different composition in natural and artificial sea water. We find that the Zn leaching from the plastic particles is reduced up to five times in artificial sea water, and this can have an effect in the toxicological studies derived. Indeed, we observe different effects in the development of
C. intestinalis when using leachates in natural or artificial sea water. We also observe that not all artificial sea waters are suitable for studying the development of the tunicarte
C. intestinalis.

Our results show that, at least in this case, both types of water are not equivalent to produce plastic leachaetes and suggest that precaution should be taken when conclusions are derived from results obtained in artificial sea water.

Marine plastic contamination is a major topic of concern, and as millions of tons of plastics enter the aquatic environment every year, researchers are trying to identify their threats both in the field and in laboratory experiments. One key possible ecotoxic route is via the formation of leachates, when chemicals associated to plastics are released into sea water. These leachates increase the threat to marine biota in all life stages, from embryos, which usually develop in the water column, to adults. Multiple studies have used laboratory experiments to determine the toxic effect of plastic leachates, using either natural or artificial sea water as equivalent solvents to obtain plastic leachates. Here we show that this equivalence may not always be the case, and explain why the use of artificial sea water may not fully represent environmental conditions in laboratory experiments.