1. Introduction
Comprising 22% of the global land mass, mountainous terrains are home to 13% of the global population, out of which ~16% reside more than 2500 m above the mean sea level (msl) [
1,
2,
3,
4,
5,
6,
7]. Glaciers, located in these mountainous terrains, act as a fresh water resource and fulfill the water-related requirements of about half of the global population. However, these fresh water reservoirs are undergoing rapid changes due to human interference-induced climate change, infrastructure development, industrialization, and tourism. The increased in-flow of tourists, in glaciated areas, is usually complemented by the intensified biomass burning, transportation and vehicular density. Fossil fuels’-driven vehicles emit several toxic compounds such as volatile organic compounds (VOCs), heavy metals, poly aromatic hydrocarbons (PAHs), elemental carbon (EC) etc., ref. [
1]. In this way, vehicular emissions contaminate the different environmental media of the glaciated terrains [
8,
9,
10,
11,
12,
13,
14].
EC, among other toxicants, is also resistant to several atmospheric degradation pathways i.e., photo-induced, chemical and biological degradation. Hence, it is susceptible to long range atmospheric transport and can even travel miles away from the source of emission [
15,
16,
17,
18,
19,
20,
21,
22,
23,
24,
25,
26,
27]. EC has a cancer potency factor equivalent to carcinogenic compounds such as benzo[a]pyrene, and upon being bio-accumulated in the environment it can affect human health [
26]. EC, compared to other particulates, it has smaller size and can penetrate through the walls of the respiratory organs and enter into the blood stream of the body and reach other organs [
8,
21,
22,
26,
27,
28,
29,
30,
31,
32,
33,
34,
35,
36,
37,
38,
39,
40]. Moreover, EC can disturb the autonomic nervous system and, subsequently, increase the susceptibility of the heart to fatal dysrhythmias [
3,
9,
10,
21,
22]. EC, emitted from diesel-driven vehicles, has also been reported to induce lung cancer and blood cancer in human sand, therefore, people in occupations involving frequent transportation and travelling are more susceptible to such cancers [
14,
23,
24,
25]. In a meta-analysis performed by Cohen and Higgins (1995), it was revealed that exhaust from a diesel engine comprising EC has a similar relative risk as that of cigarette smoke [
6]. However, the issue of the compromised health of the residents of the Indian Western Himalayas (IWHs), due to increased tourism, vehicular density and contamination of environment with EC, still needs to be addressed.
The IWHs is a landlocked area which receives emissions from urban regions of India such as Delhi, Raipur, Gwalior and Lucknow. These urban areas of India are listed among the world’s top ten most polluted cities [
26]. The Indo-Gangetic plains (IGPs) are also one of the neighboring areas of the IWHs. Several sources of emission such as stubble burning, forest fires, etc., are located in the IGPs and hence were also reported to significantly contribute in the atmospheric concentration of EC in the IWHs [
20,
32,
41]. Currently, the tough terrain of the IWHs are also connected with the metropolitan cities of the India because of increased tourism and economic activity [
12]. The increase in tourists also contaminates the pristine surroundings of the mountainous landscapes through activities such as, fossil fuel combustion, domestic-biomass burning, vehicular emissions, etc. [
11,
13,
28] In this way, the atmospheric conditions of the IWHs also get contaminated with a high concentration of EC [
31]. A study conducted at Nagpur showed that a significant amount of EC was present in snow samples of this region [
18,
19].
A scientific analysis has been performed to identify the scope of various studies carried out in the area of cancer due to excessive vehicular emission. The keyword analysis chart (
Figure 1) indicates that significant work has been performed in the area of exhaust gas, occupational exposure and lung diseases. However, lesser work has been done on the domains of air composition and cancer risk assessment in tourist places. Limited research work has been done on Indian tourist cities regarding cancer risk and vehicular emissions. In the harsh weather conditions of the IWHs, tourism is the most promising way for the residents to earn their livelihood. However, due to the uncontrolled inflow of tourists in this region, drastic impacts on the ecosystem and environment were observed [
30].
Therefore, the current study focuses on estimating the tourism carrying capacity (TCC) of one of the world-famous tourist spots of the IWHs, i.e., Manali, Himachal Pradesh, India. Furthermore, to compliment the findings of the study from a health point of view, various samples of different environmental media, i.e., water and ambient air, were collected near the snout of the Hamta glacier which is located near Manali. The lifetime carcinogenic and non-carcinogenic risk assessment of the residents exposed to the contaminated environment of the study area was also estimated. The findings of this study may provide the required impetus in framing the required policies to encourage eco-tourism so that the health disorders linked with human exposure to toxic emissions can be minimized.
4. Results and Discussion
Lifetime cancer risk from an EC-contaminated atmosphere was estimated for adults and children. The results did not depict any significant effect, however, with the current rate of EC emissions. Regardless, a future carcinogenic impact can be assumed.
4.1. Tourism Potential Regions
The identified tourism potential regions in Manali are categorized into three regions i.e., high TP region, medium TP region and low TP region on the basis of the indicators described earlier in the article.
High TP region: This consists of the most famous tourist spots in the Manali. This region comprises Manali city (i.e., Mall Road area), Rohtang Pass and the Solang Valley. These spots attract the largest number of domestic and foreign tourists in the Manali. This region fulfils most of the basic needs of the tourists due to which increases its popularity. Along with infrastructure and transportation facilities this region is also rich in social and cultural amenities and famous tourist spots such as Mall Road, the Sports Complex, the Hadimba Temple and water sports, etc., Rohtang Pass is guarded by snow covered mountains. It is also famous as it is world’s highest road that can accommodate motorized vehicles, adding adventure to the excitement of the tourists. The calm, relaxing and leisurely lifestyle in this region adds a true spirit to hill station. Solang Valley is very famous among tourists for its adventure sports such as horse riding, skiing and.
Medium TP region: The areas in this region are suitable for hiking and also have religious places located at high altitudes, where physical strength is required to reach them. According to the present study, Medium TP regions are the Jogni Falls, Beas Kund and Hamtah Pass. These places are endowed with natural beauty. They are mainly visited by professionals. Foreign tourists are attracted because of the adventure and isolation and other facilities that it offers.
Low TP region: Due to lack of infrastructure and lack of accessibility, very few tourists are attracted to this region. High altitude tourist spots, valleys, glaciated areas and hiking treks are the destinations that fall in this region. Some of the important spots of this region are Hanuman Tibba trek, Deo Tibba trek, Jagatsukh Trek, and the Jagatsukh Glacier, etc. In such tourist spots the main tourist attractions are snow, glaciers, snow covered peaks, and camp fires in the wild.
4.2. Estimating the Tourism Carrying Capacity
The TCC was evaluated to find out the highest number of tourists that Manali can handle. The values of the different variables required for the estimation of the TCC of Manali are shown in
Table 6.
According to
Table 6, it was inferred that the TCC for Manali is 300,000 tourists/month. However, it was reported that tourist flow varies significantly throughout the whole of the year, and therefore in this study a comparison of monthly tourist flow for the year 2017 in Manali with its TCC was done, and the results are shown in
Figure 5.
Figure 5 shows that the number of tourists visiting Manali is below the TCC throughout the year except for a few months. Furthermore, it can also be seen that during the months of April, May, June and October, the flow of tourists surpassed the TCC of Manali. During these months, various urban management problems such as traffic jams, the unavailability of rooms, the littering of solid waste etc., are faced by the local authorities. In the trekking spots of the low TP regions, large amounts of deforestation resulting from lodging and camp fires was reported. The unmanageable generation of solid waste and wastewater from hotels was also a matter of concern.
4.3. Carcinogenic Health Impacts of EC
The concentration of EC in different environmental media is mentioned in
Table 7.
From
Table 7, it is evident that the water body receiving water from Hamta glacier was reported to be contaminated with 19.02 ppb to 54 ppb of EC. Water from these contaminated streams was used by human beings for drinking and bathing, thus exposing them to EC. Other than that, the atmospheric EC was observed to be contaminated with 880 ± 43 µg/m
3 of the EC. This contaminated air, when inhaled by human beings. Can become deposited in the lungs, thus making them susceptible to health issues. Hence, human beings get exposed to EC via three pathways i.e., ingestion, inhalation and dermal absorption. In present study, life time cancer risk assessment was investigated to estimate the carcinogenic impacts of EC on humans (adults and children). The results obtained via this investigation are shown in
Table 8.
It is evident from
Table 8 that EC, at its present deposition rate, did not pose carcinogenic health impacts on adults. However, the lifetime cancer risk for children was reported to be <10
−6 in cases of ingestion and inhalation. Therefore, children are prone to carcinogenic and health effects from being exposed to a contaminated environment. It has also been reported that in the previous few years the number of cancer patients was also on rise, and such a trend can be associated with the contamination of the environment with carcinogenic compounds [
12]. It should be noted that when the value of the lifetime cancer risk is less than 10
–6, the carcinogenic impacts can be speculated. However, when the value is closer or between 10
–4 and 10
–6, non-carcinogenic health impacts may be the only ones that occur. Therefore, with the increasing air pollution and emission of EC, the value of the lifetime cancer risk can be presumed to increase. In this way, an EC-contaminated environment may affect human health in mountainous regions.
If strict measures are not adopted to prevent vehicle emissions, the residents of the area under study are more susceptible to serious health issues. Hence, it is recommended that other travel vehicles, such as bicycles, should be promoted to reduce vehicular emissions in mountainous terrain.
5. Conclusions
The study has been conducted to evaluate the associated cancer risk due to environmental conditions in the Indian Himalayas. The findings of the present study reflected that Manali comprises three types of tourism potential regions, i.e., high, medium and low TP regions. Among the high TP regions are Manali city (i.e., the Mall Road area), the Rohtang Pass and Solang Valley. Therefore, the TCC of Manali city was evaluated, and it was found that the threshold for the TCC of Manali was 300,000 tourists/month. In 2017, the number of tourists visiting Manali was observed to surpass this threshold in the months of April, May and June. During these months, fossil fuels-powered vehicles were also used to support the tourism industry and the contamination of different environmental media with carcinogenic compounds such as EC was also observed near the Hamta glacier. Contamination of the various environmental media with EC did not pose substantial carcinogenic health impacts on adults. However, children were reported to be more susceptible to health risks and a further increase in the atmospheric concentration of the EC in the IWHs can prove harmful for the regional community. There is a need to take corrective measures for the sustainable and controlled development of tourism in this region.