By Vijay Bhatia, Joseph Mockus and Adam Eyring
Philadelphia Water Department Bureau of Laboratory Services
September 3, 2019
The Philadelphia Water Department has been interested in water pollution caused by plastics for decades. Most of the litter in our city’s natural environment is plastic. More recently we have been studying the potential impact of microplastics: they are a source of pollution that may affect aquatic life – the health of the river is important to our goal of a healthy environment in Philadelphia; they may be a component of the particle load that may appear in water from a variety of sources; and microplastic precursors such as non-flushable wet wipes may build up in the wastewater system and, therefore, increase treatment costs due to clogs. This article highlights the current state of microplastics research.
What are microplastics? Microplastics are synthetic solid particles or polymeric matrices, with regular or irregular shapes and with sizes less than 5 mm, of either primary or secondary manufacturing origin, which are insoluble in water.
Where do they come from? Microplastics can be divided into primary and secondary fractions. Primary microplastics are manufactured as microbeads, capsules, fibers, pellets, etc. Examples include microbeads used in cosmetics and personal care products, industrial scrubbers used for abrasive blast cleaning, synthetic fibers used in textiles, and virgin resin pellets used in plastic manufacturing. Secondary microplastics are the products of breakdown of macroplastics – e.g., plastic bottles, bags, synthetic clothing, and car parts. It is estimated that 75% of the microplastics found in the marine environment are a result of breakdown of larger plastic materials by the combined action of UV radiation, mechanical forces in the sea and/or biological activity. Direct release of microplastic particles from household items, personal care products, and industrial cleaning products into our waterways via urban wastewater treatment account for significant concentrations of microplastics in water. Other factors that contribute to microplastics include the accidental loss of industrial raw materials during trans-shipment. Microplastics are pervasive globally, throughout all our eco-systems, whether marine or terrestrial. It is estimated that by 2050, 12 billion metric tons of plastic waste will be in our eco-systems in comparison to 4.9 billion tons found in 2015.
What are their health hazards? Though microplastics are known to have some negative effects on organisms in the environment, these studies have been done in laboratories at concentrations higher in magnitude than those found in natural habitats. In marine animals, microplastics at far higher concentrations are reported to alter gene expression, cause inflammation in tissues and affect reproductive success. Evidence regarding the effects of microplastics on populations of organisms in rivers, streams and freshwater is scarce. Research is needed to understand how microplastic pollution in our rivers and streams affect survival, reproduction, and the interactions between different species in a community. Not much data is available on dose-response studies over a range of microplastic concentrations as is normally done in risk assessment studies. The impact of microplastics on human health is still an emerging field.
Indirect health concerns are based on the potential for microplastics to be carriers of persistent trace chemicals as well as transporting microorganisms. It is important to note that our exposure to microplastics is all encompassing – we find them in water, beverages, foods, air, dust, soil, and everywhere. This is a bigger issue than just our water.
Are microplastics regulated in water? No, but there have been various actions taken to control their presence in the waters of the US (other countries and Europe have taken their own actions). A ban on microbeads in consumer products in the US became effective in 2018. Various towns have enacted bans or restrictions on the use of plastic shopping bags. California Senate Bill 1422, which was signed into law in September 2018, requires the State Water Board to develop plans for quantifying microplastic particles in water by 2021. Similarly, California Senate Bill 1263, also signed into law in September 2018, requires the California Ocean Protection Council to adopt and implement a statewide strategy for illuminating the ecological risks of microplastics in marine environments.
How are microplastics sampled? Methods of sampling microplastics in water or sediment depends not only on the availability of the equipment but also on the objectives of the planned research work. Microplastic sampling in water is usually done using a variety of nets or sieves, especially in flowing streams. Grab samples using large bottles are effective for water that is stagnant or flowing from a tap. Sampling of microplastic particles in sediment can be done by collection of sediment samples using a grab sampler or a box corer.
What analytical methods are available? The analysis step involves the use of modern instruments such as GC-MS, Raman, and micro-FTIR, which offer high sensitivity, rapid data collection, enhanced spectral precision, and high reproducibility. Basic analysis using microscopy and FTIR can be useful for larger particles (at least 1 mm). Because of the ability of fibers to hover in air, they have a high cross contamination potential which can introduce error during microplastic analysis.
Is there a way to reduce microplastics in water? Studies have shown that basic wastewater treatment removes the majority of microplastics, therefore reducing loads into receiving streams; however, microplastics can persist in the sludge when disposed of or applied to land as a soil amendment. Various technologies have been put into practice in streams to remove macro-plastics, however, the reduction of microplastics must begin with a reduction in the use of primary plastics and their capture for recycling, as well as in the reduction of litter. Reduction of microplastics such as wet wipes would also help since they often are involved in the formation of massive clogs in sewer systems that are expensive to remove, and their decomposition leads to microplastics.
Vijay and Joe (left two) are analytical chemists who have been developing methods for microplastics and applying them to a variety of matrices to fine-tune the methods. Adam (right) is the laboratory supervisor. All three work for the Philadelphia Water Department in the Materials Analysis Section, which has the primary task of quality control testing of water treatment chemicals and materials used by the City of Philadelphia; the lab has been expanding its capabilities into research such as microplastics as a form of water contamination.