RESUMO
The present study characterizes the dependence of microplastic consumption and excretion on particle size and body shape of fathead minnow (Pimephales promelas) over time that has not been studied. Specifically, the study is to answer four important questions: 1) how do P. promelas consume microplastic particles at different size ranges over time? 2) how long does it take for P. promelas to excrete microplastic particles after consumption? 3) do P. promelas reconsume microplastic particles after excretion? 4) are microplastic consumption and excretion by P. promelas dependent on the body shape? To answer these questions, larval P. promelas were exposed to polyethylene microbeads (PMBs) at two different consumable size ranges of 63-75 µm and 125-150 µm in moderately hard water. The experiments were designed to allow and to not allow fish to reconsume the particles they excreted. Results of the present study showed that P. promelas consumed significant amount of PMBs after 1 h of exposure to PMBs regardless particle size. The number of consumed PMBs per fish at smaller size range was up to 10 times higher than that at larger size range. When expressing the consumption in µg PMBs/fish, this difference was approximately 1.3 times, suggesting the importance of the measurement unit. After consuming, fish excreted PMBs over time and reconsumed excreted PMBs if reconsumption was allowed. Interestingly, it took longer for bent body fish to excrete PMBs than regular straight body fish. Our observation showed that excreted PMBs were likely coated with intestinal fluid that is denser than water, resulting in aggregation and deposition of PMBs. This result suggests that in the natural environment, the consumption and excretion of plastics by fish would enhance the movement of plastics from the water column to the waterbed and make it available for benthic organisms.