8.1.1. Exposure assessment
The frequency, extent and likelihood of exposure are important inputs into assessing the risks from chemicals in recreational waters. The form and frequency of recreational activity (7–8 swimming events per year in temperate climates and up to 150 swimming events per year in warmer climates; Schets, Schijven & de Roda Husman, 2011; NHMRC, 2019) will therefore play a significant role. Routes of exposure can include contact with the skin (dermal), eyes and mucous membranes; inhalation; and ingestion.
Many substances of potential concern have low water solubility and will tend to migrate to sediments, where they may accumulate. Skin exposure may occur if the sediments are disturbed and resuspended, or where recreational water users are in direct contact with sediments. Although little evidence is available, this type of exposure is considered to make only a minor contribution to overall exposure.
Dermal exposure
Skin and eye irritation result from exposure to some chemicals, including cyanobacterial toxins such as lyngbyatoxin-a (refer to Chapter 5), and alkaline and acidic substances with extreme pH (<4 or >11). Generally, irritation will be transient and resolved by washing in clean water. Causal agents are typically not identified except in the presence of harmful algal/cyanobacterial blooms (Chapter 5) or specific circumstances such as swimming in unsuitable water bodies (e.g. abandoned quarry or mine pits filled with water).
Potential health impacts from most substances depend on dermal absorption (refer to USEPA, 2004; ATSDR, 2005; enHealth, 2012). Skin is an effective barrier for many chemicals; its permeability is influenced by physical properties of the chemical. Chemicals with high permeability are typically organic chemicals of low molecular weight that are non-ionized and lipid soluble (e.g. xylene, benzene, toluene). Exposure may be exacerbated by broken or damaged skin. Dermal exposure may need to be considered if concentrations nearing guideline values, based on ingestion (refer to section 8.1.1.2), are reached for chemicals with moderate to high skin permeability. Generally, these chemicals will only be present in significant concentrations in the event of a spill. The use of wetsuits (e.g. by windsurfers, surfers, divers) can trap water inside the suit, producing a micro-environment that could potentially increase the risk of skin irritation and the absorption of chemicals through the skin (see also Chapter 5).
Ingestion
Limited data are available on volumes of water ingested during recreational activities. Estimates of volumes ingested per swimming event (95th percentiles) are 170–179 mL in children and 87–210 mL in adults in fresh waters, and 140–250 mL in children and 124–170 mL in adults in marine waters (Schets, Schijven & de Roda Husman, 2011; DeFlorio-Barker et al., 2017).
However, most hazardous chemicals cause harm following chronic exposure for many years. For example, most of the chemical guideline values in the World Health Organization Guidelines for drinking-water quality (GDWQ) are based on ingestion of 2 L per day over many years (WHO, 2017). Based on worst-case ingestion levels per swimming event of 250 mL (children) and 210 mL (adults), and estimated frequencies of eight events per year in temperate waters and 150 events in warmer waters, the volume of water ingested through recreational activities would be 2 L (children) and 1.7 L (adults) per year in temperate waters, and 38 L (children) and 32 L (adults) per year in warmer waters.
Inhalation
Inhalation can be important where there is a significant amount of spray, such as during waterskiing or whitewater canoeing. Inhalation can be of greater significance in swimming pools and related environments where chemical disinfection is practised (WHO, 2006).
8.1.2. Chemical hazards
Potential sources of chemical hazards include:
onshore and offshore industrial discharges and spills
wastewater discharges
discharges from contaminated sites
local use of motorized crafts
petroleum receiving stations
pesticides
mining wastes
naturally occurring chemicals, including algal toxins.
Information on past industry in the recreational water catchment area will give an indication of whether contaminated sediments are likely to be present and the identity of possible contaminants.
For recreational water users, risks associated with chemical hazards will depend on the type and concentration of the chemical contaminants, and the characteristics of the area. Isolated upland lakes and drinking-water reservoirs used for recreational activities are typically protected from chemical contamination. River flows, and tidal and wave action can dilute and disperse chemical discharges. In contrast, slow-flowing lowland rivers and lowland lakes may be more susceptible to contamination and provide low levels of dilution or dispersal. Water bodies subject to continuous or intermittent discharges could accumulate contaminated sediments.
Oil spills and uncontrolled discharges of industrial and mining waste waters have the potential to release high concentrations of petroleum hydrocarbons and dissolved metals and metalloids. In many cases, spills and discharges have substantial impacts on aesthetic quality of receiving waters that lead to avoidance by recreational users.
In most cases, with the exception of spills, unregulated industrial discharges and accidental discharges, chemical exposures will be well below guideline values in the GDWQ (WHO, 2017), which are based on ingestion of 2 L of water per day – this is well above ingestion associated with recreational activities.
Excluding algal toxins (refer to Chapter 5), significant concentrations of naturally occurring chemical hazards in most surface waters are less likely than contamination by industrial, agricultural and municipal pollution. However, small recreational water bodies containing water from mineral-rich strata could contain high concentrations of some substances under some circumstances. Aesthetic degradation of the water (refer to Chapter 9) is the most likely scenario – for example, as a result of contamination with metals, such as iron.
Chemical mixtures
Chemicals in natural fresh and marine waters are always present in mixtures. However, separate guideline values are calculated for most chemicals of public health significance without consideration of additive effects, and synergistic or antagonistic interactions. For many chemicals, this is appropriate for a number of reasons.
Differences in mechanisms of toxicity mean that interactions are unlikely.
The large uncertainty included in the calculation of individual guideline values is considered sufficiently conservative to account for unexpected interactions.
It is unusual for hazardous chemicals to be continuously present at concentrations at or near their guideline values.
Exposures through recreational water are also low and intermittent compared with, for example, exposures from chemicals in drinking-water.
However, there may be occasions when a number of chemical hazards with similar toxicological mechanisms are present. In such cases, potential impacts of chemical mixtures need to be considered (WHO, 2017, 2019). Where necessary, guidance on chemical mixtures in source water and drinking-water (WHO, 2017) can be applied to recreational water.
Microplastics
Waste plastics make up about 80% of all marine debris. The most visible impacts are effects on marine wildlife, and aesthetic impacts on beaches and shorelines. Microplastics have been detected at concentrations of 0–103 particles/L in fresh water (WHO, 2019). Concentrations in marine water can vary over a wide range; the average global concentration is estimated as 0.2–0.9 × 103 particles/L, and concentrations can be up to 9–16 particles/L in surface ocean water (Lusher, 2015; Everaert et al., 2018).
A review of microplastics in drinking-water found no evidence of human health risks associated with their ingestion (WHO, 2019). Levels of exposure to chemicals associated with microplastics in drinking-water are very small compared with the exposures leading to toxicity, and the relative contribution of pathogens and biofilms attached to microplastics in drinking-water is insignificant compared with other sources. This also applies to fresh and marine waters.
The much lower ingestion of water associated with recreational activities compared with drinking-water also reduces any potential risks associated with microplastics.
8.1.3. Risk assessment
Information on the pattern and type of recreational uses of the water will indicate the degree of contact with the water, and whether there is a significant risk of ingestion or inhalation of aerosols.
Chemical analysis will be required to support a quantitative risk assessment if contamination is present and there is significant exposure of users. The sampling programme should take into account variation in contamination with time and water movement. If resources are limited and the situation is complex, samples should first be taken at the point considered to give rise to the worst-case scenario; only if this gives rise to concern is there a need for wider sampling.
Quantitative risk assessments should consider the anticipated exposure in terms of both dose (e.g. whether there is significant ingestion) and frequency of exposure. The assessment should also consider the form of the contaminant, particularly for inorganic chemicals. For example, the form of metals detected can significantly influence solubility and absorption.
Example 8.1Potential PFAS contamination in Australia
Historical use of firefighting foams at Australian Government Air Force bases has been identified as a potential source of per- and polyfluoroalkyl substances (PFAS) in surface waters. Extensive environmental and health investigations and assessments have been instigated. Initial risk assessments showed that off-site migration of these substances through groundwater and across-surface stormwater flows was likely. Streams, drainage channels and impoundments were identified as potential receptors. The water bodies were generally slow moving in summer, and some were used for swimming and other recreational activities.
The initial assessment found that potential health risks associated with PFAS arise from ingestion; dermal absorption and inhalation were not considered significant sources of exposure (NHMRC, 2019). Precautionary advice was issued for the public to avoid recreational contact that might lead to accidental ingestion from potentially contaminated surface waters while investigations were undertaken. Warning signs were installed.
Health-based guideline values were developed for investigation of potentially contaminated sites in 2016 (Australian Government Department of Health, 2016). Guideline values for recreational activity (0.7 µg/L for PFOS/PFHxS; 5.6 µg/L for PFOA) were set at 10 times drinking-water guideline values, based on the approach described in the 2003 WHO Guidelines for safe recreational water environments: volume 1 – coastal and fresh waters. In 2019, the guideline values were replaced using a more refined analysis of exposure, based on ingestion volumes per swimming event (200 mL) and a conservative estimate of the annual frequency of swimming events per person (150 events per year) (NHMRC, 2019). Guideline values were set at 2 µg/L for PFOS/PFHxS and 10 µg/L for PFOA.
The formal setting of guideline values for recreational use of surface waters provided certainty for assessment of public health risks. Exceedances have been detected in drains and creeks near defence bases, although the number of exceedances has been reduced by the increase in the guideline value concentrations published in 2019. Exceedances have not been detected in larger bodies of water, such as coastal waters.
Communities are being informed about results, and advice is issued about surface waters (generally drains and creeks) that are not suitable for recreational use.
Source: Australian investigations (http://www.defence.gov.au/environment/pfas/).
Except for spills and unregulated discharges, it is unlikely that water users will come into contact with sufficiently high concentrations of chemical contaminants to cause adverse effects following a single exposure. Even repeated exposure is unlikely to result in adverse effects at the concentrations of chemicals typically found in surface water.
Example 8.1 provides a case study relating to surface water contamination with per- and polyfluoroalkyl substances.
Some water bodies will be assessed as being permanently unsuitable for recreational contact – for example, quarries and abandoned mine pits that have filled with water. These will typically contain high concentrations of the mineral being extracted, may contain high concentrations of chemicals used in extraction processes, and can have very high or low pH. Quarry and pit lakes can contain metals (e.g. iron, aluminium, manganese, lead, copper, cadmium, nickel, zinc) and metalloids (e.g. arsenic, antimony). They can contain water with pH <3 (Nancucheo et al., 2017; Petrounias et al., 2019), and limestone quarry lakes can contain water with pH >11. Swimming in waters with pH >11 or <4 can cause irritation of the eyes, skin and mucous membranes.
Chemical spills
Oils spills can release complex mixtures of chemicals, primarily hydrocarbons. Most are not soluble and spills produce large, visible floating slicks that discourage recreational exposure. A common feature of the soluble hydrocarbons (e.g. toluene, ethylbenzene, xylenes) is the production of distinctive tastes and odours at concentrations that are well below those that represent health concerns (WHO 2008, 2017). These tastes and odours will render water unsuitable for recreational use. Studies of human health impacts of oil spills have largely focused on impacts on clean-up volunteers and communities living near the site of spills, rather than exposure through recreational use of the waters (Aguilera et al., 2010).
Uncontrolled discharges from industrial and mine sites can release high concentrations of chemicals such as metals and metalloids into receiving waters (Nancucheo et al., 2017; Petrounias et al., 2019). Mine wastewaters can have a pH <3 or >11. Uncontrolled discharges often cause visible and distinct discolouration of receiving waters.
