What lurks in ships’ ballast?

Plastics and microplastics are ubiquitous in the oceans and provide both a substratum and

substrate for microbes.  Plastics adsorb and concentrate metals and toxic chemicals

(including antibiotics) by a factor up to 10⁶.  It has been shown that co- and cross-resistance

result in co-selection, meaning that exposure to one metal/toxin/antibiotic can result in the rapid evolution of microbial tolerance or resistance to multiple others.

This review highlights microplastics in ballast water as a source and vector for toxic compounds.  The transport of pathogens between continents is concerning and we know, for example, that Vibrio cholerae was dispersed in ballast water from Asia to Latin America. Biofilm formers do well on internal tank surfaces so it is reasonable to propose that may also be true for microplastic particles.  Ships’ ballast tanks are closed systems within which microbes are exposed to a cocktail of toxic compounds and it is plausible that this environment could significantly increase pathogen virulence. 

However, the key limitation in the paper is that we do not yet have evidence to show that microplastics in ballast increase microbial virulence.  Therefore the authors’ call to amend the Ballast Water Management Convention seems premature, but certainly more urgent research is needed.  

NAIK, R. K. et al. 2019. Microplastics in ballast water as an emerging source and vector for harmful chemicals, antibiotics, metals, bacterial pathogens and HAB species: A potential risk to the marine environment and human health. Marine pollution bulletin, 149, 110525.