6.3.2 Organic compounds (Revised 2011)

Organic compounds are usually present in drinking water in very low concentrations. They may occur either naturally or as a result of human activities. By-products of disinfection are the most commonly found organic contaminants in Australian drinking water supplies. Pesticides and petroleum products are occasionally detected in source water or treated drinking water in Australia, but rarely at concentrations above health-based guideline values.

Disinfection by-products

The by-products of disinfection are the products of reactions between disinfectants, particularly chlorine, and naturally occurring organic material such as humic and fulvic acids, which result from the decay of vegetable and animal matter. Of these disinfection by-products, the trihalomethanes (THMs) are produced in the highest concentrations.

Most disinfectants used to render drinking water safe from pathogenic microorganisms will produce by-products in the disinfection process. Factors affecting the formation of disinfection by-products include:

• the amount of natural organic matter present;

• the disinfectant used;

• the disinfectant dose;

• pH;

• temperature;

• the time available for reaction (contact time).

Chlorine is the most common disinfectant; in the chlorination process it reacts with naturally occurring organic matter to produce a complex mixture of by-products, including a wide variety of halogenated compounds (i.e. organic by-products of chlorination). The main by-products are the THMs and chlorinated acetic acids. Many other by-products can be produced, but concentrations are generally very low (usually <0.01 mg/L and often <0.001 mg/L).

Other disinfectants can produce different types of by-products: for example, ozone is known to produce formaldehyde and other aldehydes.

Known disinfection by-products are considered individually in the fact sheets in Part V. It is possible, however, that other disinfection by-products for which no health data are available are present at extremely low concentrations. It is also possible that when these compounds (both known and unknown) are ingested together, their combined effects on health may be different from their individual effects. Epidemiological studies examine disinfection by-products as a generic group, and can be useful in determining overall effects.

A number of epidemiological studies have suggested an association between water chlorination by-products and various cancers (Michaud et al. 2007, Villanueva et al. 2007). This association has been most consistent in relation to cancer of the bladder and rectum, but there are insufficient data to determine concentrations at which chlorination by-products might cause an increased risk to human health.

In experiments with laboratory mice, when concentrates derived from chlorinated drinking water were applied to the skin, there was no increase in the incidence of skin tumours compared with concentrates derived from unchlorinated supplies. Similarly, oral administration of chlorinated humic acids in drinking water did not increase the incidence of tumours compared with animals receiving unchlorinated humic acids, or with saline-treated controls (IARC 1991).

Studies have shown that concentrates of some chlorinated drinking water supplies are mutagenic to some strains of test bacteria. These effects were consistently found with samples of surface water that had a high content of natural organic compounds at the time of chlorination. A significant proportion of the increased mutagenicity has been attributed to a chlorinated furanone known as MX (Kronberg and Vartiainen 1988).

The International Agency for Research on Cancer has reviewed the available data and concluded that there is inadequate evidence to determine the carcinogenicity of chlorinated drinking water to humans (IARC 1991).

Action to reduce the concentration of disinfection by-products is encouraged, but disinfection itself must not be compromised: the risk posed by disinfection by-products is considerably smaller than the risk posed by the presence of pathogenic microorganisms in water that has not been disinfected.

Further information on disinfection of drinking water is contained in the information sheets (Part IV) and fact sheets (Part V).

Pesticides

For the purpose of the Guidelines the term ‘pesticides’ includes agricultural chemicals such as insecticides, herbicides, nematicides, rodenticides and miticides.

The Australian Pesticides and Veterinary Medicines Authority (APVMA) is responsible for assessing all pesticides prior to registration to allow sale and use in Australia. For registration, data required on the pesticide include information on the proposed use, the toxicity and the residues that might result from proper use. When the pesticide is registered, a safe level of exposure, conditions of use and maximum levels of residues for water are determined. This mechanism allows the formulation of appropriate guideline values for pesticides in drinking water and a process for their revision, which includes public consultation.

The use of pesticides in Australia is regulated by the states and territories, though this is the subject of a COAG reform and may change in the future. The APVMA provides label requirements for the approved use and application of pesticides and these labels are required to be followed by all users of registered pesticides, with enforcement the responsibility of the states and territories. These label requirements are intended, in part, to minimise pesticide contamination of waterways. Consistent with this, pesticides should not be found in water supplies above safe levels and if they are, investigations must be undertaken to determine how they came to be there. These investigations should then be followed by corrective action aimed at the prevention of pesticide contamination of drinking water supplies.

Within the context of aiming to minimize pesticide contamination of drinking water, it should be noted that a small number of pesticides have been approved by the APVMA for the management and control of pests including insects and insect larvae in drinking water supplies. An example is s-methoprene, which has been approved for use as a larvacide in rainwater tanks. In circumstances where pesticides are intentionally applied to drinking water supplies, drinking water concentrations should be monitored to ensure that concentrations are within safe levels.

Contamination of drinking water by pesticides may occur occasionally as a result of accidental spills, misadventure, or emergency use of pesticides. In such cases, prompt action may be required by public health officials.

The health-based guideline values are derived from the acceptable daily intake (ADI) and are set at about 10 per cent of the ADI for an adult weight of 70 kg and a daily water consumption of 2 litres. The health-based guideline values are very conservative, and include a range of safety factors, which always err on the side of safety.

In earlier versions of the Australian Drinking Water Guidelines, the guideline value for many pesticides was set at the practical analytical detection limit for the particular chemical substance. This approach was used to reflect the philosophy that good water quality management should aim to prevent the contamination of drinking water supplies by pesticides (regardless of potentially negligible health implications). While this management philosophy still applies, the approach to setting guidelines has been revised and analytical detection limits are no longer used as guideline values for pesticides.

The revised approach has been adopted for two main reasons. The first is that analytical detection limits are constantly changing (decreasing) as a result of on-going technological advancements. This means that in order to keep up-to-date, a detection limit-based guideline would also need to be continuously revised downward, which is an impractical situation from a human health perspective. The second reason is the desirability of a scientifically-consistent approach to guideline setting across all chemicals. Wherever possible, guideline values for all other chemicals are based on human health considerations and toxicological data. Accordingly, it is appropriate that the guideline values for pesticides be addressed in the same way.

As noted above, this change in guideline setting for pesticides does not change the general philosophy regarding the management of pesticides in drinking water supplies. Persistent detection of pesticides may indicate inappropriate use or accidental spillage, and investigation is required in line with established procedures in the risk management plan for the particular water source.

Pharmaceuticals and endocrine-disrupting chemicals

Pharmaceuticals

Pharmaceuticals comprise a large class of predominantly organic compounds. They are administered to humans and animals to achieve a variety of benefits including prevention and treatment of disease. The large variety of compounds in use and their importance to physiology, along with their widespread use and chemical characteristics contributing to persistence suggest the potential for their similarly widespread distribution in the environment and the potential for contamination of potable water supplies.

Virtually all pharmaceuticals administered to humans are excreted in varying degrees and discharged directly into the sewerage system. These compounds are then affected by treatment processes in municipal sewage treatment plants, before discharge to the environment. Depending on chemical properties including aqueous solubility, volatility, lipophilicity and susceptibility to biodegradation, pharmaceutical residues may be removed in varying degrees during conventional sewage treatment processes prior to environmental discharge.

Synthetic pharmaceutical compounds were first observed and reported in sewage during the 1970s. Since then, over 100 pharmaceutical drugs and metabolites have been identified in environmental samples, primarily in Europe and North America. Reported compounds include analgesic, anti-inflammatory, beta-blocker, lipid regulator, antiepileptic, b2-sympathomimetic, antineoplastic, antibiotic and contraceptive drugs.

No definitive link has been reported or established between pharmaceutical exposure in drinking waters and human health risk. Furthermore, current evidence does not support a general requirement for additional or specialised drinking water treatment to reduce concentrations of pharmaceuticals. Routine monitoring is not recommended, but targeted, well designed and quality controlled investigative studies could provide more information on potential human exposure from drinking water. Nonetheless, concern for the potential implications of exposure to mixtures of these biologically active chemicals exists and worldwide investigations are ongoing.

Specific concerns have been raised by some scientists that the presence of antibiotic agents in water supplies may facilitate the development of resistant organisms, with implications for public health (Kummerer 2009). While this may be a valid hypothesis, studies are yet to demonstrate that the presence of antibiotics in water supplies has any impact on the development of resistance.

It is not common international practice to regulate or provide guidelines for pharmaceuticals in drinking water. However, the Australian National Guidelines for Water Recycling (Phase 2): Augmentation of Drinking Water Supplies have taken a pro-active approach and do provide guideline concentrations (and an approach for further developing guidelines) that are applicable to potable water supplies intentionally augmented by recycled municipal effluents (EPHC, NHMRC and NRMMC 2008). Use of these guideline values should be considered for supplies where the risk assessment identifies significant contribution of municipal effluent, whether it is intentional or unintentional.

Endocrine-disrupting chemicals

During the last few decades, reports of hormonally related abnormalities in a wide range of species have accumulated. Chemical contaminants are believed to be responsible for many of these abnormalities, acting via mechanisms leading to alteration in endocrine function. This phenomenon, known generally as ‘endocrine disruption’, has been identified by the World Health Organization as an issue of global concern (Damstra et al. 2002). The chemicals implicated have been collectively termed ‘endocrine-disrupting chemicals’, or simply ‘endocrine disruptors’ (Damstra et al. 2002).

A particularly well documented form of endocrine disruption has been the induction of biochemical hormonal responses in freshwater fish, which can cause significant behavioural and morphological dysfunctions and lead in the worse cases to sterility (Tyler and Jobling 2008). A growing number of natural and synthetic environmental chemicals have been implicated as causative agents of these observed disruptions. However, in terms of potency, the most significant have been natural and synthetic steroidal hormones. Some steroidal hormones have been observed to cause disruption of the endocrine system of fish at ambient concentrations less than 0.000001 mg/L (1 ng/L).

Environmental exposure to oestrogenic hormones has been shown to cause feminisation of male fish (Tyler and Jobling 2008, Rempel et al. 2006. More recently, exposure to androgens has been implicated in the masculinisation of fish (Jensen 2006). Furthermore, scientists suspect that anthropogenic estrogens, androgens and progestins may act as reproductive pheromones in fish, thus adversely affecting reproduction (Kolodziej et al. 2004).

Much attention has focused on the discharge of hormonal steroids from municipal sewage treatment plants. Municipal sewage effluents have been generally characterised as being ‘oestrogenic’ in nature, due largely to trace concentrations of oestrogenic steroidal hormones as well as some other natural and synthetic chemicals.

While some endocrine-disrupting chemicals have been detected in some drinking water supplies, concentrations have been generally insignificant compared to other dietary sources of estrogenic activity.

Box 6.1

The Black Mountain Declaration (2007) on Endocrine Disrupting Chemicals in Australian Waters

Humans, as mammals, have very similar endocrine systems to other species for which impacts of environmental endocrine-disrupting chemicals (EDCs) have been observed. There is clear evidence that humans have been severely impacted by some EDCs when exposed to significant doses in the form of medications or extreme occupational exposure. However, exposure to EDCs via water (either through recreation or consumption) is considered relatively insignificant compared to other sources such as occupational or dietary exposure.

Despite the valid reasons for concern, evidence of impacts to humans from environmental exposure to EDCs is yet to be established. This includes a lack of evidence of impacts via exposure from water supplies, food products and air. Given the observed susceptibility of other species and the ultimate importance of protecting public health, a precautionary approach towards minimising unnecessary exposure to EDCs in water, food and air is warranted.

It is not common international practice to regulate or provide guidelines for endocrine-disrupting chemicals in drinking water. However, the Australian National Guidelines for Water Recycling (Phase 2): Augmentation of Drinking Water Supplies have taken a pro-active approach and do provide guideline concentrations (and an approach for further developing guidelines) that are applicable to potable water supplies intentionally augmented by recycled municipal effluents (EPHC, NHMRC and NRMMC 2008). Use of these guideline values should be considered for supplies where the risk assessment identifies significant contribution of municipal effluent, whether it is intentional or unintentional.

Other organic compounds

Naturally occurring organic compounds are not generally of human health concern, except for certain specific toxins (see fact sheets on Toxic Cyanobacteria). Other than disinfection by-products, organic contaminants resulting from human activity are not normally detected in Australian drinking water. They have, however, been detected at times in supplies in North America and Europe, usually following an accidental spill or discharge into a water source or, on rare occasions, from rain contaminated by airborne pollutants. Fact sheets and guideline values are provided in case similar incidents should occur in Australia.