Page - 13 - in Freshwater Microplastics - Emerging Environmental Contaminants?

a power and had undergone artificial weathering, using a L/S of 10 and a 72 h leachingtime, to themarineharpacticoidcopepodNitocraspinipes.Here, leachates fromdifferentPVCmaterialsdiffered in their toxicity,with the toxicityof leachate from PVC packaging increasing after artificial weathering; whereas the leachate from PVC garden hose material decreased after artificial weathering [99]. This study also showed that the leachable PVCconstituteswere a complexmixture of substances, and interestinglymass fragments containing chlorinewere not identi- fied. There are many challenges associated with the characterisation of such leachatesowing to thepotentialdiversityofphysicochemicalproperties that chem- icalmigrants andbreakdownproductsmayhave.A test protocol for the identifica- tion of migration products from food contact materials has been developed that combines LC-TOF-MS and GC-MS techniques that generate accurate mass and predictedformulae toscreenforvolatile, semi-volatile, andnon-volatilesubstances [100, 101]. Overall, theL/S ratioofplasticmaterial used in these studies ishigher than that typically identifiedduringenvironmentalmonitoringstudies.However, this typeof screeningwhen applied tomaterialsmanufactured fromhazardousmonomers and additivescouldfacilitate theidentificationofcompoundsof interest sothat theycan be effectively replaced. 6.3 BiologicalEffects of Sub-micrometerPlastics Depending on their use, plastic materials can contain compounds such as anti- microbialagentsandnanomaterials thatmaybe toxic toorganismssuchasbacteria and fungi that play a critical role in ecosystem functioning. It is possible that a combination of microscopic particles, leached additives, and other degradation products may cause subtle effects towards aquatic and terrestrial organisms that are difficult to identify in current testingmethodologies. The formation of plastic particles in the submicron and nanometer size range during degradation is highly likely [8, 40, 66, 102, 103].Engineerednanoparticles (ENPs) are able to cross cell membranesandbecomeinternalised,andtheuptakeofENPsissizedependentwith uptakeoccurringbyendocytosis or phagocytosis [104].Once inside the cellENPs are stored insidevesicles andmitochondriaandable toexert a response [104].Cel- lular responses include oxidative stress, antioxidant activity, and cytotoxicity [105]. In termsof toxicity assessments, there is aneed tounderstand themolecular andcellular pathwaysand thekinetics of absorption, distribution,metabolism, and excretion mechanisms that may be unique toMPs in the nano-size range. Desai et al. [106] showed that 100 nm particles of a polylactic polyglycolic acid co- polymer had a tenfold higher intracellular uptake in an in vitro cell culturewhen compared to 10 μm particles made of the same material. ENPs have also been shown to produce cytotoxic, genotoxic, inflammatory, and oxidative stress responses in mammalian and fish systems [107]. A literature review by Handy MicroplasticsAreContaminants ofEmergingConcern inFreshwater. . . 13