A new study has found that chemical additives in everyday plastic might be stopping – or, at best, interrupting – the reproductive habits of a shrimp-like species that is key to the marine food chain. The findings provide a different perspective on the potential damage caused by specific pollutants.
Much of the research into the effect of plastics on marine and freshwater life has focused on large particles and visible plastic and has focused on vertebrates. Researchers from the University of Portsmouth in the UK have, instead, looked at how the additives found in everyday plastics can negatively impact the sex life of a key invertebrate aquatic species.
“These creatures are commonly found on European shores, where they make up a substantial amount of the diet of fish and birds,” said Alex Ford, the study’s corresponding author. “If they are compromised, it will have an effect on the whole food chain.”
The creature to which Ford is referring is Echinogammarus marinus, a shrimp-like creature or amphipod, found on coastlines from Norway to southern Portugal. Precopulatory pairing – forming pairs to reproduce – is a common mate-guarding strategy observed in the species that is imperative for mating success. It’s been used in previous studies as a quantitative measure of the impact of various compounds on mating by recording the time taken for the disruption and reformation of pairs. Pairs of E. marinus typically lock together for up to two days while mating.
In the current study, the researchers investigated the impact of four plastic additives on the precopulatory pairing behavior and sperm count of E. marinus. The additives they considered included two plasticizers, n-butyl benzenesulfonamide (NBBS) and triphenyl phosphate (TPHP), and two phthalates, diethylhexyl phthalate (DEHP) and dibutyl phthalate (DBP).
“We chose these four additives because the suspected danger they pose to human health is well-documented,” said Bidemi Green-Ojo, lead author of the study. “Two of the chemicals (DHP and DEHP) are regulated and not allowed to be used in products in Europe. The other two chemicals have no current restrictions on them and are found in many household products. We wanted to test the effects these chemicals had on aquatic mating behavior.”
DEHP and DBP are found in medical supplies, food packaging and toys. TPHP is mainly used as a flame retardant in products like nail polish, children’s products and electronic equipment, whereas NBBS can be found in nylon, medical devices and cooking utensils.
A total of 480 pairs were exposed to one of the four additives, each at six different concentrations, including two controls. Exposure was carried out in rectangular dishes with a separator. The males and corresponding females were isolated on opposite sides of the separator then, after one hour of exposure, the separator was removed. The researchers measured contact time (unsuccessful attempts at establishing a precopulatory pair) and re-pairing time (time taken for the successful formation of a precopulatory pair).
They found that exposure to all chemical additives prolonged contact and re-pairing times. The effect on re-pairing was concentration-dependent, with re-pairing rates reduced by around 30% at 5 µg/L and by more than 50% at concentrations above 5 µg/L. These concentrations are lower than those previously reported in some freshwater and marine systems in Europe and Asia. Increased concentrations of the plastic additives tested drastically reduced the proportion of pairs that re-paired. The researchers observed that animals that hadn’t paired within a day or two didn’t do so over the next two to three days.
In E. marinus exposed to TPHP and DBP for 14 days, sperm count declined with increasing concentrations. However, exposure to NBBS and DEHP did not show a concentration-response relationship.
“This unsuccessful mating behavior has serious repercussions, not only for the species being tested but potentially for the population as a whole,” Ford said. “These animals form pairs to reproduce. Once they were exposed to a chemical, they would break apart from their mate and take much longer – in some cases days – to re-pair, and sometimes not at all.”
The researchers say that studies like this provide a different perspective on the potential damage caused by specific pollutants.
“We must understand more about these chemicals and how they affect behavior,” said Green-Ojo. “Many types of behavior – such as feeding, fight or flight mode, and reproduction – are essential in an animal’s life, and any abnormal behavior may reduce the chances of survival.”
The study was published in the journal Environmental Pollution.
Source: University of Portsmouth
