Fluoride Levels in Canary Islands Tap Water

A total of 274 samples were collected in Gran Canaria and Tenerife islands from Canary Islands archipelago, 78 of those were taken in the former and 196 in the latter one (Table 1) (Figure 1). Three replicates were taken from each sampling point. Gran Canaria’s sampling locations were divided in four areas based on demography and topography, meanwhile only three zones were created in Tenerife. The Table 2 summarized the water sources of the collected samples.
The island of Tenerife (28°16′07″ N 16°36′20″ W), is the largest and most populated of the Canary archipelago. The drinking water supply of the island of Tenerife is based on rainwater infiltrations that pass through the island’s generally porous volcanic soil and accumulate in underground galleries. The island of Gran Canaria (27°57′31″ N 15°35′33″ W), is the second most populated island of the Canary Islands. According to the Hydrological Plan of Gran Canaria, around 50% of the island’s water resources come from seawater desalination, while water extracted from underground galleries only represents 35% and a 15% from surface water sources [23 ].
The Canary Islands are an archipelago with a volcanic origin. Volcanism is one of the most important factors in the occurrence of fluorides in water [24 (link),25 (link)]. This study has chosen two of the volcanic islands where the presence of fluorides in their water has previously been found, especially in Tenerife [26 (link),27 (link),28 (link),29 ]. It is indisputable that population is linked to water demand, so a high inhabitants density generates overexploitation of its water resources. In relation to island aquifers, when natural recharge from rainfall is lower than reserves, this could lead to a significant increase in fluoride levels [30 ].
In addition, the recent eruptions In the Canary Islands (submarine eruption of the Tagoro Volcano on El Hierro in October 2011, terrestrial eruption of the Tajogaite Volcano on La Palma in September 2021) together with the unified model of the origin of the Canary Islands proposed by Anguita and Hernan [31 (link)], highlights the importance of adequate monitoring and control of the island’ water supply.
The sampling locations are showed in the Figure 2. The samples consist of tap water collected from different businesses and private homes by allowing the water to flow for 5 min prior to collection. In addition, these samples were collected in airtight plastic containers, to avoid the loss of fluoride by ionic diffusion in silicates. These containers were kept cold and the analysis were performed within a period not exceeding 5 days after collection.