Phytoremediation

A plant based solution to clean our soil and water

Research conducted for Company New Heroes, Biobased CreationsDate: June 30 2021Author: Fatema Bahernwala, Naturecentric

Plants produce the oxygen we breathe; release volatile organic compounds that enhance our mood and lower our blood pressure (Antonelli et al., 2020). Being in green spaces improves our mental health and allows us to relax and focus better (Aerts, Honnay, & Van Nieuwenhuyse, 2018; Ma, Zhou, Lei, Wen, & Htun, 2019; Wood, Hooper, Foster, & Bull, 2017). Plants also play an important role in the regulation of the fresh water cycle and help us capture precious rain water and store it underground. Moreover, they provide us with all the food we eat directly and indirectly by feeding the animals we eat. They are an important source of medicine and building materials. And now, we are also learning now their essential role in cleaning up the soil beneath our feet.

As much as plants need soil to survive, the soil is actively shaped by the plants and other creatures that live in it. It is a truly symbiotic relationship. When we incorporate plants in and around our homes, we acknowledge their essential role in our lives.

This is becoming increasingly important as the world urbanizes and more than half of the global population lives in cities today (Hannah Ritchie & Max Roser, 2018). Our habitats are increasingly becoming concrete and steel jungles. Living in these built up areas often exposes people to pollution of different kinds, especially air, water, soil and noise pollution. Pollution not only has an impact on human health but also on biodiversity.

A CBS survey in 2018 found that concern for the nature is growing in the Netherlands and 75% of the Dutch people think Nature has been severely damaged. Over half thought that air, soil and water are polluted in the Netherlands (CBS, 2018).

AIR

The Netherlands ranks the 2nd highest in the EU in terms of artificial land cover (built-up land + artificial non built up areas) (EU EIR, 2019) and this has an impact on air quality. Amsterdam and Schiphol are the amongst the most polluted places in the Netherlands in terms of air and noise pollution. Air pollution in the Netherlands costs 13 months of life for an average person due to exposure to particulate matter and nitrogen dioxide (NO2).

An obvious solution is to reduce the source of pollutions – the number of vehicles on the road and planes in the air and the amount of fertilizer added to agricultural land. In addition to that increasing vegetation by planting more trees, plants and mosses that absorb particulate matter from the air will help clean the air we breathe.

Balcony or backyard gardens; greening tree pits and paved areas should be considered where possible. In addition, Roof gardens and Moss walls are not only visually appealing but also take up little space in cramped urban areas. The biobased home includes good examples of these.

water

The Netherlands is blessed with plenty of water and drinking and bathing water are of good quality. However, human activities have been polluting the water bodies and as of 2019, only 2 water bodies in the Netherlands were of good ecological status (EU EIR, 2019).

In terms of water pollution, more than three-fourths (78%) of surface water bodies in the Netherlands are affected by the diffuse from agricultural sources, mainly fertilizer and pesticide run off from agricultural lands. This fertilizer run off leads to nutrient pollution in our water bodies by loading the water bodies with excess nutrients that lead to algal blooms and reduce the oxygen in the water body – often resulting in the death of other aquatic life.

Algal bloom in an Amsterdam canal

Nutrient pollution has one of the most significant impacts on surface water categories in the Netherlands, where 65 % of surface water bodies affected, followed by altered habitats: 75 %, and chemical and organic pollution: around 50% (EU EIR, 2019). This includes medicines such as pain killers, blood pressure reducers and antibiotics leached into the water.

Plants such as cattail and reed grasses help clean up water while they provide a habitat for aquatic life. A win-win situation that ultimately supports biodiversity and reduces pollution.

Plant profile: Cattail

Cattails are found growing by the water in the Americas and Europe and are one of nature’s best water filters and shoreline protectors. These perennial plants grow upto 10 feet tall (Jackie Rhoades, 2021). The flower and seed pod of this plant looks like a hot dog. They have an extensive root system that prevent erosion and removes sediment from water. Cattails are very useful when it comes to removing toxic substances from water such as mercury and arsenic; human medications; as well as nutrients such as phosphorous, which in excess quantities leads to algal blooms (Tinham, 2012).

They provide shelter, nesting material and food for a variety of wildlife, including insects; tiny fish and other small aquatic creatures that birds and other wildlife feed on.

They are edible – their young stems, roots and flower heads can be eaten and used for medicinal purposes. In addition, they were used to make furniture; weave baskets and mats and use as stuffing for life jackets in WWII (Jackie Rhoades, 2021).

While they are not so easy to grow indoors or in pots; they proliferate in their natural habitats such as lakes; ponds or canals where they grow relatively easily.

Cattail. Image source: ejernigan Pixabay

Plant profile: Reeds

Reeds constitute different types of grasses found in shallow water or wet soil in most parts of the world including Europe (PFAF, n.d.).

Reed swamps fulfil important functions in their local ecology: these grasses stabilize water bank and are very useful in disspating wave energy be used for shore protection or flood control; their roots stabilize sediment and provide conditions for microbial decomposition of external organic load, that is nitrates and other nitrogen loads in water thus aiding the elimination or fixation of nutrients (pollution control) and reduce chemical oxygen demand (PFAF, n.d.; Randerson, Davies, & Bialowiec, 2010; Wolfgang Ostendorp, 1993). Thus, they are very useful in cleaning sewage water.

Reeds. Image: Hans Braxmeier Pixabay

The roots and shoots of reeds are edible and the roots were commonly cooked like potatoes. All parts of the plant can also be used medicinally for symptoms ranging from vomiting due to food poisoning to coughing. They can also be burnt as fuel (biomass); used a fertilizer; upholstery filler, weaving baskets; making paper, string or ropes (PFAF, n.d.).

SOIL

Industrial activities that release chemicals in our water bodies and land; fossil fuel processing; and agricultural effluents coming from excessive fertilizer and pesticide use are among the leading causes of soil pollution. This is not a developing world problem alone – as of 2014, there were approximately 250,000 sites in the Netherlands showing various degrees of soil pollution. Of these, 1,518 sites were seriously polluted and unacceptable human and ecological risks.

Number of sites in the Netherlands with contaminated soil. Image source: RIVM

In the city of Amsterdam itself, while conducting this research I came across 4 polluted sites in the area of Amsterdam Noord (Amsterdam North) where the soil is too polluted to grow food and in some neighbourhoods so polluted that residents have to leave their backyards tiled.

Of course, the Dutch government cleans this soil – mostly using the conventional approach of transporting it and treating it using thermal and chemical processes. Roughly 2 million tons of soil is cleaned annually in the Netherlands using mostly offsite industrial processes. These technical processes are expensive, costing approximately Euros 100 to 250 per cubic meter of soil (Grondverzet.nu, n.d.), which costs in the range of 250 million Euros per year , as well as energy intensive, often using fossil fuels, which paradoxically, is one of the pollutants of soil. Moreover, these processes kill all life in the soil, resulting in dead soil.

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However, soil is a living entity teeming with life. Each gram of soil consists of millions of organisms including earthworms, nematodes, mites, insects, fungi, bacteria and other microorganisms (SoilSolution.org, n.d.). Thus, an alternate way to tackle the problem of soil pollution is by enlisting the help of other creatures - that is to get plants, bacteria, and fungi to clean and regenerate our soil and water. This method is much slower and much more environmentally friendly and cost effective.

Using plants and soil microbiota (bacteria and fungi in the soil) to clean contaminated soil and groundwater often on-site (on location) is called phytoremediation. The word phytoremediation comes from the Greek word phyto (plant), and the Latin word remedium (restoring balance) (Phillips, 2019). Through this process contaminants are either absorbed (phytoextraction); degraded into simpler non-toxic molecules (phytodegradation and/or phytovolatization) or immobilized (phytostabilization) thus cleaning up the environment and reducing the risk of further contamination via air, rain water flow, or other natural processes as shown in the diagram below.

Types of Phytoremediation. Source: Naturecentric, 2021

Sounds interesting? It is! The type of phytoremediation and the duration it takes to clean up the soil depends on the type of contamination. Nitrates, chlorinated solvents, hyrdocarbons (petroleum products) and pesticides are cleaned up relatively quickly, while heavy metals take a much longer time to stabilize within the plant body.

When we think of phytoremediation, sunflowers often come to mind. Sunflowers were used to absorb radioactive isotopes/ nucleiods at Chernobyl after the power plant meltdown in the 1990s. Many commonly available plants such as poplars, willows, sunflowers, different grasses (reeds and miscanthus, corn) and legumes such as alfalfa have amazing abilities to extract, stabilize (in roots), or degrade pollutants in the soil.

Once these plants have absorbed these contaminants, the next question that arises is, what do we do with these plants? In situations where the pollutant is degraded into non-toxic by-products, it is not much of an issue and the plant or tree can continue to provide other ecosystem functions, namely clean air and supporting biodiversity in its new home. However, when we are dealing with phytoextraction, where for example, heavy metals have been absorbed within the plant, consumption of the plant by birds, animals and humans could be potentially harmful. This is something still being investigated by scientists. However, in the meantime, here is a list of things we can do with the plants after remediation:

Composting if the pollutant is degraded by the plant and the resulting plant body is non-toxic.
Controlled Incineration where the plant is used as a biofuel in a controlled environment and then extract heavy metals from emissions and ashes.
Make products such as paper and cardboard (depending on type of contamination of soil and amount extracted by plant).

Use as a construction material in a biobased home.

Plants such as hemp, flax, poplar and cattail not only assist in remediating soil but also make good building material. This is a really good use of the plant after phytoremediation. Check out the biobased creations website or visit them at the Dutch Design Week or at Floriade to see which plant based materials are used in the construction of the home.

PHYTOREMEDIATION IN ACTION

Westergasfabriek

There are some examples of where you can find phytoremediation in action. On a visit to Westergasfabriek in Amsterdam, you can see how Willow trees have been used to clean up an industrial site where the soil and ground water was polluted from a former coal and gas factory that was operational from 1885 to early 1990s. The site left heavily polluted with tar, cyanide, asbestos and heavy metals. In 1997, landscape architects Kathryn Gustafson and Francine Houben designed a plan to restore the contaminated land and convert it into the cultural space that is vibrant today.