Abstract:
The ubiquitous presence of microplastics across all aquatic ecosystems, stemming from plastic
pollution, necessitates their classification as emerging contaminants. This widespread
distribution is concerning due to the propensity of aquatic organisms to ingest microplastics,
this behavior likely arises from the similarity between microplastics and natural organic matter
suspended in the water column. The current study investigated the toxicological impacts of
microplastics of three prevalent plastic polymers—high-density polyethylene (HDPE), lowdensity
polyethylene (LDPE), and polypropylene (PP) on the freshwater crustacean Daphnia
magna in mono exposure and co-exposure settings. The microplastics ranging size 0-32 μm
were synthesized in the laboratory in concentrations ranging from 30 to 150 mg/l. The lethal
concentration 50 (LC50) for combined exposure was determined to be 77 mg/L, contrasting
with LC50 values of 120 mg/L, 123 mg/L, and 109 mg/L for exposures to PP, LDPE, and
HDPE alone, respectively. This variability in toxicity levels is attributed to the differential
densities of the polymers and the distinct preferences of Daphnia magna for specific polymers
within the aquatic environment. Co-exposure also induced a 10% increase in microplastic
ingestion due to compromised egestion mechanisms, alongside a 21% reduction in
reproductive rates due to impaired reproductive functionality under stress-induced conditions.
Furthermore, combined exposure resulted in reduced population densities, with LDPE
exhibiting the highest absorption rates at lower concentrations, followed by HDPE and PP at
higher concentrations. Moreover, Daphnia exhibited extreme erratic swimming patterns
indicative of heightened behavioral stress under combined exposure conditions relative to
singular exposures. These findings underscore the potential threat that synergistic interactions
