The mass of tire particles in the ocean is expected to represent 93% of the aquatic plastic contamination by 2040. This might have consequences on organisms, like physical injuries and health repercussions notably due to chemical risk following the leaching of tire -associated chemicals. In such context, it is pivotal to assess the risk posed by this stressor in marine living organisms and aquaculture activities in the context of long-term chronic exposure scenarios. In the present study, a multidisciplinary and multigenerational approach was implemented in the Pacific oyster Crassostrea gigas , a species having a high economic value and an important ecological role in the ecosystem functioning. To assess the effects of particles and leachates, several endpoints reflecting different organization levels were investigated.
Material and Methods
The e ffects of tire particles, tire leachates and natural particles were investigated at individual scale (generation G0) over a 6 weeks exposure in a flow-through system using endpoints reflecting different organization levels (e.g. transcriptomic analyses, gut microbiota, tissue alterations, feeding activity, growth, reproductive outputs) up to offspring performance (e.g. development, fertilization rate, larval growth). Secondly, the G1 offspring performance (development, survival and growth of larvae and juveniles) was monitored over one year up to their ability to reproduce (G2 larval progenies), providing unprecedented views about the potential long-term risks from exposure to tire particles at environmentally relevant concentrations for marine organisms.
No significant differences in ecophysiological parameters and haemocytes features were observed between exposed parental conditions whereas molecular analyses revealed the disruption of energy metabolism and stress response following leachates exposure. Oocytes had the highest number of differentially expressed genes; among these, many were associated with endocrine disruption and demonstrated that oocytes are mostly targeted in case of prolonged exposures of the broodstock during gametogenesis. Microbiota analysis revealed the over-representation of Tenacibaculum spp., a gram-negative and motile bacterial genus often associated with mortality events of marine animals, which suggested the onset of dysbiosis following exposure to high concentration of both tire particles and leachates. Parental exposure had an impact on gamete quality with a 22% reduction of motile spermatozoa in the leachate conditions but had no consequences on the fertilization success nor lead to long-term effects on offspring growth and reproductive outputs. Considering the concept of energy-limited tolerance to stress, it would be of great interest to test tire risk in the context of harsher natural conditions (e.g. food limitation, water quality).
Overall, w hile our results bring a positive note on the apparent resilience of Pacific oysters to tire particles exposure, caution should be taken when extrapolating these results to other rubber materials or to natural – harsher – conditions occurring in coastal ecosystems, bearing in mind that the first answer to plastic pollution is to reduce its production and usages whenever possible and favor durable materials.