Pollution, Microplastics and Caring for Country

A substance is a pollutant because of how much of it there is and where it ends up, not because of what it is. Nitrogen fertiliser is exactly what a wheat crop needs; the same nitrogen washed into a river feeds an algal bloom that kills the fish. Heat, noise and light can pollute too: warm water released from a power station lowers the oxygen a river can hold, and bright coastal lights lead hatchling turtles away from the sea.

Scientists trace a pollutant through three stages. The source is where it is released, the pathway is how it travels (air, water, soil, or inside living things), and the receptor is the organism or ecosystem it harms. Break any link in that chain and the harm stops, which is why the model is useful for designing solutions, not just for describing problems.

Sources come in two kinds, and the difference decides how hard a problem is to fix. A point source releases pollution from one identifiable place, such as a factory outlet, a sewage treatment plant or a smelter chimney, so it can be measured, licensed and fined. A diffuse (non-point) source is spread across thousands of small contributors: fertiliser from many farms, oil and tyre dust washed off every road in a city, exhaust from millions of cars. No single contributor looks significant, so diffuse pollution is much harder to regulate, and it is now the larger problem in most Australian waterways.

Almost all of it traces back to a handful of human activities. Burning fossil fuels for electricity and transport releases fine particles, nitrogen oxides and sulfur dioxide. Agriculture releases fertilisers, pesticides and eroded sediment. Mining and smelting release heavy metals: at Port Pirie in South Australia, lead from a smelter that has operated for more than a century has left many local children with blood lead levels above the national guideline. Cities add stormwater, litter and wastewater. Some pollutants break down within days; others, such as heavy metals, which are elements and cannot break down at all, and synthetic chemicals like PFAS, persist for decades.

The implications of pollution are rarely the direct poisoning people imagine. More often the pollutant sets off a chain of events inside an ecosystem, and the harm arrives several steps later. Two chains explain a large share of the damage.

Eutrophication starts with too many nutrients. Nitrate and phosphate from fertiliser or sewage reach still or slow-moving water, and algae, which were limited by those nutrients, multiply into a bloom. The bloom shades out seagrass and other plants below it. When the algae die, bacteria decompose them, and decomposition uses up the dissolved oxygen in the water. Fish, crayfish and mussels suffocate. Some blooms are cyanobacteria (blue-green algae) that also release toxins, which is why waterways are closed to swimming and stock drinking. In 1991 a cyanobacterial bloom stretched about 1,000 km along the Darling River, and the NSW Government declared a state of emergency.

Biomagnification happens with pollutants that are persistent (they do not break down) and stored in fat rather than excreted, such as mercury and the insecticide DDT. Plankton absorb a tiny amount. A small fish eats thousands of plankton and keeps all of their pollutant; a larger fish eats hundreds of small fish; a bird or shark at the top eats many of those. At each step the concentration rises, so the top predator can carry millions of times the concentration found in the water. DDT thinned the eggshells of birds of prey until their eggs cracked under the parent, which is one reason it was banned in Australian agriculture. It is also why Food Standards Australia New Zealand advises pregnant women to limit shark (flake) and billfish such as swordfish, which are top predators and accumulate mercury.

The implications therefore spread across four areas: ecosystems (fish kills, lost seagrass, collapsing bird populations), human health (the World Health Organization estimates that air pollution causes about seven million premature deaths each year), the economy (closed fisheries, clean-up costs, lost tourism) and communities and culture, including Aboriginal and Torres Strait Islander communities whose food sources and cultural practices depend on the health of particular waters on Country.

A microplastic is any piece of plastic smaller than 5 mm. Some are made or released at that size, and these are called primary microplastics: synthetic fibres that shed from polyester and nylon clothing in the wash, dust worn off car tyres on the road, the pre-production pellets (nurdles) from which plastic products are moulded, and the microbeads once added to face scrubs. Others are secondary microplastics, formed when a bottle, bag or fishing net is broken into smaller and smaller pieces by ultraviolet light, heat and wave action. Plastic fragments, but it does not biodegrade on any human timescale, so the pieces keep getting smaller without disappearing.

The link to human activity is unusually direct, because plastic does not occur in nature: every particle has a human source. An International Union for Conservation of Nature study in 2017 estimated that synthetic textiles and tyre wear together make up roughly two thirds of the primary microplastic reaching the ocean. That points to two ordinary activities, washing clothes and driving, rather than only to littering. The pathways are just as human. Wastewater treatment plants remove most fibres from laundry water, but the fibres they capture end up in sewage sludge, which is often spread on farmland as fertiliser. Tyre dust and street litter are washed into untreated stormwater drains and carried straight to rivers and the sea.

Once there, microplastics are eaten by the smallest animals in the food web. Zooplankton, filter-feeding mussels and small fish mistake them for food, which can fill the gut without providing energy. Plastic also carries chemical additives and adsorbs other persistent pollutants onto its surface, so it may deliver them to the animals that swallow it. On Lord Howe Island, Australian researchers found that flesh-footed shearwater chicks are fed plastic by their parents, and in 2023 they described scarring of the chicks' stomach tissue caused by plastic, which they named plasticosis. Microplastics have now been detected in seafood, drinking water, table salt and human blood.

What scientists do not yet know matters just as much. There is not yet clear evidence of the effect of microplastics on human health, and measurements are hard to compare because different laboratories count different size ranges. An honest discussion of the link between human activity and this pollution concern says both things: the source is certainly human, and the full size of the harm is still being measured. In 2020, CSIRO scientists used seafloor sediment samples from the Great Australian Bight to estimate that about 14 million tonnes of microplastic now lie on the ocean floor worldwide.

Aboriginal and Torres Strait Islander Peoples have lived on and cared for Country for at least 60,000 years, through ice ages, rising seas and major changes in climate. Harvesting food and materials over that length of time without exhausting them required detailed knowledge of how each species breeds, grows and responds to being taken. There are hundreds of distinct nations, each with its own Country, languages and practices, so the examples below belong to particular peoples and should not be read as one single "Aboriginal practice". Many of these practices continue today.

Budj Bim, Gunditjmara Country (south-west Victoria). The Gunditjmara people built a system of channels, weirs and ponds into the lava flows around Lake Condah (Tae Rak) to trap, hold and harvest kooyang, the short-finned eel. Parts of the system have been dated to at least 6,600 years old, which makes it one of the oldest known aquaculture systems in the world. Water levels were managed so that eels moving through the channels could be held alive in ponds and taken when they were needed, and eels were smoked to preserve them. In 2019 the Budj Bim Cultural Landscape became the first place in Australia to be added to the UNESCO World Heritage List for its Aboriginal cultural values alone. It is managed today by Gunditjmara Traditional Owners.

Baiame's Ngunnhu, the Brewarrina fish traps, Ngemba Country (north-west NSW). On the Barwon River, a network of dry-stone walls forms ponds and channels across the riverbed. Ngemba tradition tells that the creator ancestor Baiame designed the traps and gave each family group a particular trap to use and a responsibility to maintain it, along with rules for their use. Fish swimming upstream enter the ponds and are held there alive, so people could take what they needed and release the rest. Neighbouring nations were invited to share the traps at certain times. The site was added to the National Heritage List in 2005.

The same logic appears in everyday harvesting. When digging yams, harvesters in several regions replaced the top of the tuber in the ground so that the plant would regrow. People gathering eggs took some and left the rest so the birds would keep breeding. Harvesting was timed by seasonal calendars that read signals in the environment, such as the flowering of a particular plant, which told people when an animal was fat and ready to eat, or when it was breeding and should be left alone.

Each of these practices encodes an ecological understanding that Western science describes in its own terms: leave enough of the breeding population for it to replace itself; give a harvested area time to recover; match harvesting to the organism's life cycle; and make particular people responsible for a resource so that nobody takes more than their share. These understandings were built from generations of close observation, tested over thousands of years, and passed on through story, song, ceremony and practice.

A harvesting practice says how to take something sustainably. A Cultural protocol says who may take it, where, when, how much, and what they owe in return. Protocols are grounded in the Law of each nation, and they are what turns good ecological knowledge into sustainable use by a whole community over many generations. Without shared rules, even people who understand an ecosystem well can overharvest it when everyone acts alone.

Protocols govern access: people from outside a group seek permission from the Traditional Owners before entering Country or taking its resources. They govern responsibility: in many nations a person or clan has a totem, an animal or plant to which they have a special connection and obligations, which can include not eating it and protecting the places it lives. Because different people hold different totems, responsibility for many species is spread across a whole community. They govern timing and quantity: some species may not be hunted while breeding, some places are rested, and a catch is shared along kinship lines so that taking more than is needed has no benefit.

In the Torres Strait, dugong and green turtle are central to Island culture and diet, and hunting them continues under native title rights. Torres Strait Islander communities have written their own community-based dugong and turtle management plans, supported by the Torres Strait Regional Authority, which set local rules such as which areas are closed, how many animals may be taken, and that nothing taken may be wasted. Torres Strait Islander rangers monitor seagrass, turtle nesting and dugong numbers, so the protocols are informed by data as well as by tradition.

Protocols also apply to knowledge itself. Ecological knowledge belongs to the communities who hold it; some is shared publicly, and some is restricted and may only be known by certain people. Scientists who work with Aboriginal and Torres Strait Islander communities follow the AIATSIS Code of Ethics (2020), which requires free, prior and informed consent, acknowledgement of knowledge-holders, and fair sharing of benefits. The practices described in this lesson are ones that their custodians have chosen to share publicly, for example through heritage listings.

Most pollution in this lesson comes from a linear pattern of resource use: extract a material, make a product, use it briefly, throw it away. The alternatives are ranked in the order they appear in the phrase, because each one avoids more extraction, manufacturing energy and waste than the next. Lesson 9 described what happens inside recycling; here the question is how the three options compare, and why recycling comes last.

Reduce means not using the resource in the first place, and it is the only option that prevents every stage of impact. It includes designing products to use less material, buying fewer and longer-lasting things, and removing single-use items entirely: from 2022, NSW banned single-use plastic straws, cutlery and lightweight plastic bags. For microplastics, reducing works at the source, for example washing-machine filters that catch fibres before they reach the drain, which France has required in new washing machines from 2025.

Reuse keeps a product working for longer: refillable bottles, repair, hand-me-downs and second-hand markets. The product's manufacturing impact has already been paid, so each extra use spreads it more thinly. Recycle recovers the material but not the product, and it costs energy for collection, sorting and reprocessing, which is why it sits last.

The ranking is a guide, not a guarantee, and this is where the discussion has to be careful. A reusable product is only better if it is actually reused enough times. A life-cycle assessment by the UK Environment Agency (2011) compared shopping bags on their contribution to climate change: a paper bag had to be used about 3 times, and a cotton bag about 131 times, before its climate impact was lower than that of a conventional plastic bag used once without secondary reuse. The heavier reusable bag carries a larger manufacturing impact that only repeated use pays back. The plastic bag still does more damage as litter and microplastic, so the "best" choice depends on which impact is being measured. Australia's National Waste Policy Action Plan (updated in 2024) sets targets that combine all three strategies, including a 10% reduction in waste generated per person and an average 80% resource recovery rate by 2030.