Canadian recreational water quality guidelines - Indicators of fecal contamination: Water for secondary contact activities
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The Guidelines for Canadian Recreational Water Quality are intended to be protective for those activities that involve intentional or incidental immersion in natural waters. Recreational water activities that have been traditionally considered secondary contact activities (for example, canoeing, kayaking and fishing) involve different exposures from those associated with primary contact uses. A recent meta-analysis found a significant increase in GI associated with primary contact activities (swimming, sports-related water activities), but a non-significant increase in risk with secondary contact activities involving minimal water contact (Russo et al., 2020). Secondary contact activities are presumed to result in a lower ingestion of water and therefore a lower risk of GI. Although secondary contact activities are associated with lower risk, inadvertent immersion can result in whole body contact and splashing can lead to a variety of water exposure scenarios. Illnesses affecting the skin and perhaps the mucous membranes of the eyes and ears may be of relatively greater importance for secondary contact uses (U.S. EPA, 2002). Inhalation may also be an important route of exposure during primary and secondary contact activities in areas where splash, spray or aerosols are generated.
There has been limited research on the differences in exposures between primary and secondary water contact activities. A study by Dorevitch et al. (2011) estimated that the average volume of water ingested during secondary contact activities was approximately 3 to 4 mL/h, in comparison to primary contact activities with ranges between 10 and 40 mL/h (Dorevitch et al., 2011; Dufour et al., 2017; U.S. EPA, 2019). In addition to swallowing a lower volume of water, only 1% of the individuals engaged in secondary contact activities reported swallowing water (compared to 51% of primary contact participants) (Dorevitch et al., 2011). This translates into fewer individuals being exposed during secondary contact activities. In a follow-up analysis of the Dorevitch study (2011), data on numerous human waterborne pathogens were collected and QMRA was utilized to estimate the potential human health effects during secondary contact activities like fishing, canoeing and boating. The waterway analyzed was a man-made canal system where primary contact activities were prohibited but secondary contact activities were allowed. The risk assessment model results estimated the health risks from these activities to range from 0.10 to 2.78 HCGI per 1000 incidental exposure events, which is lower than the acceptable illness risk (8 HCGI per 1000 exposures) associated with the U.S. EPA's primary contact recreational water guidelines (Rijal et al., 2011). This is consistent with an earlier study that found no significant risk of GI in individuals engaged in canoeing or rowing (Fewtrell et al., 1994). In contrast, a companion prospective cohort epidemiological study compared the health impacts of secondary contact recreation activities on the same man-made waterway (where the water quality does not meet guidelines for primary contact recreation) to the health impacts of secondary contact activities on a lake with acceptable water quality for primary contact activities. An increased risk of GI (13.7 to 15.1 illnesses per 1,000 exposures) was found in both water types (Dorevitch et al., 2012). This risk is higher than that calculated by Rijal et al. (2011) using their risk assessment model, which had several limitations associated with the pathogen datasets. Although the risk of illness was similar for the canal system and for the general-use area, the exposures for these sites were different. Recreators in the man-made canal system were less likely to report head/face submersion than their counterparts in the general-use waters. There were also more individuals fishing in the general-use waters, which is associated with a longer exposure time compared to canoeing and kayaking. Fishing has been reported elsewhere as a significant contributor to the overall risk of GI owing to the extended potential exposure time and possible routes of exposure other than ingestion (for example, hand-to-mouth transfer of pathogens) (Sunger et al., 2015).
To date, there are insufficient epidemiological data available to derive health-based fecal indicator limit values for secondary contact recreational water activities. However, because a lower degree of water exposure occurs at most times during the majority of secondary contact recreational water activities, separate secondary contact water quality values may be developed using the primary contact guidelines combined with the level of water exposure. The type of secondary contact recreational water activity and the duration of exposure will affect the level of water exposure. This approach may be considered reasonable and acceptable to local and regional authorities where a secondary contact designation is desired.
When contemplating the establishment of separate fecal indicator values for water areas used entirely for secondary contact recreation, a clear understanding of the types of activities that would fit under this description is required. The World Health Organization (WHO), in its Guidelines for Safe Recreational Water Environments: Volume 1—Coastal and Fresh Waters (WHO, 2003), has proposed a scheme for the classification of recreational water activities according to their degree of water exposure. The following descriptions (adapted from WHO, 2003), may be used as an initial guide when determining whether a specific recreational water activity would be considered primary or secondary contact:
- Primary contact: Recreational activity in which the whole body or the face and trunk are frequently immersed or the face is frequently wetted by spray, and where it is likely that some water will be swallowed. Inadvertent immersion, through being swept into the water by a wave or slipping, would also result in whole body contact. Examples include swimming, surfing, waterskiing, whitewater canoeing/rafting/kayaking, windsurfing and subsurface diving.
- Secondary contact: Recreational activity in which only the limbs are regularly wetted and in which greater contact (including swallowing water) is unusual. Examples include rowing, sailing, canoe touring and fishing.
Even if these classification criteria are used, it remains a significant challenge to discern which activities constitute primary contact and which constitute secondary contact. The classification of certain recreational water activities will be clear, whereas that of others may be less obvious and more open to interpretation. Water activities considered potential candidates under a secondary contact use designation should be evaluated on a case-by-case basis.
Other factors to consider before assigning a secondary contact use designation to a recreational water area include the following:
- The water area should first be subject to an assessment of existing uses, water quality and the potential for improvement as well as any other relevant factors, such as health or environmental considerations.
- The secondary contact designation should not be applied where an assessment has shown primary contact recreation to be a significant use.
- Where the water area has a shared use (for example, swimming and canoeing), it is the primary contact values that should apply.
- When an area is posted as suitable only for secondary contact recreational uses, communication material should clearly convey that accidental immersion (through falls, canoe spills and so on) can lead to whole body exposure. Under such circumstances, water ingestion may result in an increased risk of illness.
- Users should be reminded to take the precautions necessary to ensure that these types of exposures are avoided as much as possible. The skill of the person performing the activity may strongly influence the degree of water exposure.
In some instances, a responsible authority may choose to use a validated predictive water quality model to determine the types of water activities allowed at a site on a given day (for instance, primary or secondary contact activities), as opposed to designating the site specifically for primary or secondary contact use. Clear, consistent, and up-to-date risk messaging for recreational users would be necessary for these areas to ensure public health protection is maintained.
If it is determined that a water area is intended to be used for secondary contact recreation, a direct multiplier based on the assumed ratio difference between the primary contact exposure volume and the desired secondary exposure scenario volume can be applied to the fecal indicator guideline values. For example, using average ingestion volumes, the ratio between low ingestion activities, such as boating, fishing and canoeing/kayaking without capsizing (3.8 mL/h; Dorevitch et al., 2011) and swimming (10 mL/h to 40 mL/h; Dorevitch et al., 2011; Dufour et al., 2017; U.S. EPA, 2019) is approximately 3 to 8. The choice of multiplier should consider the sources of fecal contamination in the waters, as human fecal sources are more likely to contain human pathogens than other non-point sources of contamination. For example, in a water system that is impacted by human or ruminant fecal sources, the responsible authority may want to apply the conservative assumption of 3 times higher than the primary guideline value. This would result in a BAV of 705 cfu E. coli/100 mL for the secondary contact values. Any value calculated would represent a risk management decision based on a thorough assessment of the expected exposure scenarios and potential health risks for the recreational water user. In considering both the potential health risks and the benefits of recreational water use, it was concluded that this is a tolerable and reasonable approach to protect users engaged in a voluntary activity.
There is insufficient information available to develop secondary contact guidelines for other parameters in the Guidelines for Canadian Recreational Water Quality. Therefore, for all other parameters, the primary contact values should be applied. The development of secondary contact values should not be used as a mechanism for downgrading the status of an area in response to poor water quality issues. This is particularly important where an assessment has shown that the primary contact guideline values could be achieved.
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