Environmental Effects

Stormwater

New Zealand is one of the most urbanised countries in the world, with 73 percent of us living in cities of at least 30,000 people. ⁴⁸⁴⁰

As a result of land clearance and urban development, most of these urban areas are covered in impermeable surfaces. For example, in the Auckland region only 19 per cent of the 10,000km long stream network passes through native forest. ⁴⁸⁴¹  

In these paved and developed areas, rainwater cannot be absorbed by vegetation and soil, as it would be in rural areas. Therefore, to reduce the risk of flooding, towns and cities have stormwater systems that channel rainwater into gutters and pipes and eventually out into streams, lakes and coastal waters. Because a large number of New Zealand’s urban centres are sited on estuaries and harbours, the stormwater many towns produce discharges directly to the coast.

Stormwater systems are often a significant source of pollutants into the catchment and coastal areas because the water that enters the pipe network picks up and carries with it a wide range of contaminants from the streets, industrial and construction sites, roofs and other surfaces. These substances include heavy metals (especially zinc, copper and lead – lead contamination has been falling since lead was removed from petrol but zinc contamination continues to rise) ⁴⁸⁴² hydrocarbons from vehicles (these come from the road surface itself, exhaust emissions, brake linings and tyre wear), sediment and contaminated dust. ⁴⁸⁴³

Roof run-off is a major source of zinc contamination in catchments which have been urbanised for a long time, because of the large number of galvanized iron roofs in poor or unpainted condition. Zinc oxide used in tyres is another. In addition, urban earthworks have the potential to release large amounts of sediment into the catchment. ⁴⁸⁴⁴

Waste water 

The following section is imported directly from the Ministry for the Environment Guide: Sustainable wastewater management: A handbook for smaller communities. 

Organic material 

The organic content of wastewater is made up of human faeces, protein, fat, vegetable and sugar material from food preparation, and soaps from cleaning. Some of this is dissolved into the water and some exists as separate particles.

Naturally occurring soil and water bacteria eat this organic waste and use it to grow rapidly. In a natural or dilute water environment where there is plenty of oxygen dissolved in the water, aerobic (oxygen-using) bacteria eat the organic material and form a slime of new bacterial cells and dissolved salt-waste products. If undiluted wastewater is left on its own, however, anaerobic (non-oxygen-using) bacteria decompose the waste organic material and release odorous gases such as hydrogen sulphide, as well as 'non-smelly' gases such as methane and carbon dioxide.

It is the amount of oxygen removed or the too-rapid growth of the bacterial slime that can cause the harm. Where there is an overwhelming amount of wastewater, all the oxygen will be used up and the anaerobic bacteria will take over. The water will go septic (anaerobic) and the fish will die, as will other forms of oxygen-dependent life. This is partly why wastewater is treated to remove as much organic material as possible. But the content of even treated wastewater can be an issue. Sensitive streams and estuaries are particularly vulnerable.

In effect, ecosystem services can be damaged, and these problems may be felt well before the level of pollution directly affects human health. ⁴⁸⁴⁵

Suspended solids

The portion of organic material that does not dissolve but remains suspended in the water is known as suspended solids. The level of suspended solids in untreated wastewater is around 200 g/m3.

If effluent is discharged into streams untreated, any solids it contains will tend to settle in quiet spots. Oxygen levels will soon be depleted in the area of the contamination, causing it to decompose anaerobically. If there are high concentrations of this contamination the water in the stream will go septic because the oxygen will be used up. This will not only smother the fish, but will also kill off the life at the bottom of the stream, creating dead zones.

Dissolved salts 

The most significant salts in wastewater are nitrates and phosphates. These occur naturally to some extent. Nitrate also derives from the breakdown of organic nitrogen in protein waste matter, and the oxidation of the ammonia in urine. Phosphates are present in detergents used in washing and laundering, and are also produced by organic breakdown. The total nitrate in wastewater is around 40 g/m3, and phosphate is around 15 g/m3.

Nitrates and phosphates are essential elements for growth. When nitrates and phosphates are discharged into natural waters they fertilise the growth of microscopic algae and water 'weeds', which can lead to green algal suspensions and weed mats. This overgrowth results in their death and decay, and means further consumption of dissolved oxygen and smothering of aquatic life. The nutrients that caused the initial growth can then be released back into the water, initiating another cycle of weed and algal growth and decay.

Bacteria and viruses

The human gut produces a huge quantity of bacteria, which are excreted as part of faeces on a daily basis. The most common and easily measured organism is E.coli (Escherichia coliform group), which is referred to by wastewater scientists and engineers as 'faecal coliform' bacteria. Special tests are needed to distinguish between the amount of pollution produced by humans and the amount produced by birds and other animals that gets into the water.

The main class of viruses are the enteric viruses, which cause gastro-enteritis; for example, calcivirus (Norwalk virus), rotavirus, enterovirus (polio and meningitis) and hepatitis. In a marine environment some viruses have been known to survive a number of days, possibly protected in suspended solids.

Many of the faecal coliform bacteria in human waste are harmless. However, there are disease organisms – or 'pathogens' – that can cause harm. These can be bacteria such as typhoid, or viruses such as hepatitis B. Direct contact with these pathogens or pollution of the water supply can cause infections. 

The Ministry of Health has national responsibility for developing drinking-water standards, which will guide your community's understanding of the risks it might face from local wastewater. Sewage can pollute shellfish-gathering areas and, if eaten, the shellfish will cause illness. Shellfish filter food by passing several litres of water an hour through their system. The food concentrates in the shellfish, which means that any pathogens will also accumulate.

Relatively high concentrations can also make an area unsafe for swimming and 'water contact recreation'. National guidelines developed by the Ministry for the Environment help local communities to classify their harbours, streams and lakes in terms of safety for swimming, fishing and shellfish gathering. Local regional councils will set standards for discharges for these areas. These standards relate to the amount of bacteria present in a certain volume of water.

Ground water can also become contaminated. Wastes can percolate through the soils into underground water or aquifers. Given that many smaller communities and farms obtain their water from bores or wells into these aquifers, this contamination can be a serious issue.

 Other dissolved constituents

Wastewater contains metals, chemicals and hormones from households (via food, medicines, cosmetics and cleaning products) and business processes (eg, mercury from dentistry, which can easily be removed by installing a centrifuge in dental surgeries). It can also contain halogenated hydrocarbons and aromatics, plasticisers, polyaromatic and petroleum hydrocarbons, organochlorine pesticides, PCBs and dioxins.

There are two issues: if large quantities are discharged into small, highly localised areas, such as a stream or small lake, there may be pollution problems. The other issue is the 'bio-accumulation' of these substances in various parts of the food chain. This can bring unacceptable concentrations in humans and aquatic life, which can lead to health problems.

Long-term health impacts of residues in water supplies and food

The issue here is one of long-term impacts of various wastewater residues on the human system. Water naturally contains such things as iron, zinc and manganese, but industrial processes can introduce higher concentrations. If the concentrations are high enough, exposure to some metals and chemicals may have an impact on how the body's system works.

The long-term impacts of these substances on human health are not always well understood. Wastewater will carry a range of substances, which can pass into the water supply or be returned to the soil in heavy concentrations. Some treatment systems will remove metals and chemicals from the wastewater, but the sludge produced as a result of this treatment will then contain a high concentration of these substances. 

Endocrine disruption

The endocrine system in the human body is a complex network of glands and hormones that regulate many of the body's functions, including growth, development and maturation, as well as the way various organs operate. The endocrine glands – including the pituitary, thyroid, adrenal, thymus, pancreas, ovaries and testes – release carefully measured amounts of hormones into the bloodstream, which act as natural chemical messengers. They travel to different parts of the body to control and adjust many life functions.

An endocrine disruptor is a synthetic chemical, which, when absorbed into the body, either mimics or blocks hormones and disrupts the body's normal functions. This disruption can happen through altering normal hormone levels, halting or stimulating the production of hormones, or changing the way hormones travel through the body. This is a new area of scientific investigation and is not yet well understood. There are concerns that, for example, the decline in fertility levels in all animals in the food chain, including humans, could be as a result of excessive discharge of these chemicals. Such investigations are now being considered in New Zealand.

The issue is relevant to wastewater issues because many of these substances will enter the food chain – either on land or in waterways – from wastewater. Of course some of the chemicals (eg, some pesticides) will also enter the ecosystem via run-off from farms and roadways. Wastewater treatment systems will remove some of these chemicals, but generally treatment processes are not currently designed to deal with this problem.

⁴⁸⁵³

Aquatic ecosystems

The issue raised for human health is also relevant to aquatic ecosystems. There is some concern that the hormone-producing systems in fish are under pressure. High levels of oestrogen released from wastewater can affect the reproductive cycles of fish. The degree to which this is an issue in New Zealand is not known.

These can have the immediate effect of killing fish, invertebrates and even plant life. This can be a serious loss in itself, but there are also flow-on effects. The dead fish or plants will be broken down, and can contribute to further depletion of oxygen in the water.

Soil depletion 

This is not so much an effect of something in the wastewater itself, but has more to do with how the management of nutrients in wastewater systems bypasses natural processes. It is worth discussing here because of the link with ecosystem health.

Over the last hundred years or so waste management design has favoured using water to transport wastes. It has also favoured direct disposal into rivers, lakes and the sea. The remaining sludge has tended to be landfilled. One effect has been to bypass the nutrient cycle, whereby wastes would be slowly returned to the soils to be taken up as a food source by plants. Some would enter the streams and rivers via groundwater but most would remain in the soils.

The depletion of nutrients from the soils has been raised as an issue in parallel with a wider concern with sustainable environmental management. This depletion means that if soils are to successfully support plant life (and farming), they must have nutrients returned through alternative processes. This can be costly.

In effect, bypassing the natural nutrient cycle means that many wastewater systems contribute to nutrient depletion in soils. Conversely, streams, rivers and lakes face risks from overloading with nutrients – with many of the problems mentioned earlier.

Soil structure

Sediments, metals and salts can affect soil structure. For example, sodium ions can be found in high concentrations in wastewater. If irrigated on to land they can damage soil structure.

Last updated at 12:55PM on February 11, 2018