Socio-Environmental Vulnerability of Water in the Estuary of the Metropolitan Region of Santos (Brazil)

According to the United Nations, the world population growth rate will be more pronounced in the coming decades, with an increase of 2.5–3 billion people by 2050, and with that, there will be an increase in the need for water, sanitation and hygiene (Leridon 2020). This phenomenon will boost vulnerability in socio-environmental, urban, economic and political spheres (Cutter et al. 2003). The United Nations Department of Public Information Report showed that in 2012, approximately 828 million people lived in slums with a growth rate of 6% per year (p.a.), and by 2020 it should reach 889 million in the urban migration process (UN 2012 and 2013). Coastal zones are more densely populated than inland areas and exhibit higher rates of population growth and urbanisation. The development of coastal areas has increased considerably in recent decades, producing socioeconomic changes and generating high pressure on ecosystems due to the exploitation of natural resources and pollution. Land use and urbanisation are also related to increasing population exposure and vulnerability along the coasts, especially in developing countries (Small, Nicholls 2003; Balk et al. 2009; Kron 2013; Neumann et al. 2015). In these zones, we can find vulnerable nuclei (VN), subnormal agglomerations, precarious settlements and slums, characterised by populations with low incomes and lack of access to safe drinking water, sanitation, and public housing and health policies, who live in non-conforming housing (NH) (IBGE 2010; SAO PAULO 2010; AGEM 2015; UN-BR 2018).

Port, industrial and tourist activities drive the Baixada Santista Metropolitan Region (BSMR) located in the Santos and São Vicente Estuarine Complex (SSEC) and induce invasions in flooded areas, where we find the largest slum on stilts in Brazil (Fabiano, Muniz 2010; Sampaio et al. 2011). The main actors behind this problem are the municipal governments who do not draw up adequate master plans for popular low-income occupations and parallel power organisations that rent out these irregular areas for the occupation of precarious housing. Housing changes and urban regularisation imply better sanitary conditions since the houses are now supplied by a regular water and sewage distribution system, in addition to allowing other essential services such as regular garbage collection. The improvement is a natural result of the replacement of irregular housing. The water quality of local watercourses automatically improves its indicators from the moment the raw sewage stops being deposited. Sewage discharge, inadequate waste disposal and port accidents compromise the quality of water and sediments. We analysed the population growth of VN in the SSEC and verified the water quality changes between 2005 and 2018.

The evolution of GAGR from 2005 to 2014 in urbanised areas was 0.68% p.a. in SAG and less than 1.24% p.a. BSMR and other regions of the world, such as 1.52% p.a. in Latin America and the Caribbean (LAC), are at a rate of 4.57% p.a. in sub-Saharan Africa and at a rate of 4.53% p.a. in Western Asia (IBGE 2010; UN 2016; IBGE 2018). Paradoxically, in informal areas from 2005 to 2018, GAGR_NH in SAG 74 VN was 5.60% p.a., while BSMR 525 VN reached 6.07% p.a., higher than all other areas in LAC (−0.75% p.a.), sub-Saharan Africa (3.12% p.a.) and Western Asia (3.89% p.a.) (Young, Fusco 2006; AGEM 2015; UN 2016; Annex A; Annex B). Except for Cubatão municipality, with a negative GAGR_NH (−7.95% p.a.), the municipalities of SSEC presented VN with growth types 1 and 2, in non-conforming dwellings and the occupied area or areas of verticalisation and population concentration. Intense urbanisation has significantly altered the physical environment, and the conservation of natural areas near urbanised areas remains to be considered of little importance to the government. Young 2009; Moreira et al. 2017 emphasise that the lack of conservation of natural areas in BSMR contributes strongly to environmental degradation and the impacts related to urban activities. On the other hand, in Cubatão, housing policy is based on housing production through partnerships with the state and federal governments. Some projects only include new units, while others have joint urbanisation and housing production actions. In addition to the construction of about 10,000 houses, the projects foresee urban areas occupied by families. The Organic Law of the Municipality of Cubatão establishes in Article 7(2) the municipality's concurrent competence, together with the State of São Paulo and Brazil, to execute housing production programmes. Combining this provision with the relevant chapter on municipal housing policy (Arts. 207 to 211) is the foundation in the local legal system for such sectoral policy and competence that enables the municipality to conclude agreements with other federative entities (Gillan, Charles 2019).

There are significant social impacts of daily releases of in natura effluent of approximately 2,086,000 m³ · month⁻¹, PL of 450 tonnes · month⁻¹, in addition to the inadequate disposal of garbage in water bodies (estuaries, beaches, canals and rivers), as well as the presence of emerging pollutants requiring advanced treatment that is not available from RMBS. Sewage discharges and inadequate waste disposal in the rivers’ innermost areas modify estuarine waters’ hydrodynamics and cause urban flooding, especially in the summer, when there is a more generous river contribution caused by heavy rains (Berbel et al. 2015). Other locations globally, also densely populated and with a population problem in unstable housing exposed to urban and industrial contaminants, are also affected. For instance, in India, the effects of anthropogenic stress on the Ganges River show increased biochemical oxygen demand (BOD), reduced salinity and pH, as well as the presence of high concentrations of Hg and Pb, attributed to discharges from manufacturing and industrial processes (Sarkar et al. 2007). Additionally, in India, on the Ganges delta in Bengal, there was evidence of Vibrio cholera concentrations associated with discharges, temperature and salinity of waters in the estuary (Batabyal et al. 2016). In Cameroon, cholera risk factors are associated with slums, poor sanitation and hygiene. There are high cholera risks in Douala, which demonstrates that the issue goes beyond public health to the point of a humanitarian disaster (Ndah, Ngorah 2015).

The relationship between economic growth and the release of contaminants has been known for some time. Garcia Occhipinti (1986) presented the most relevant aspects for analysing an ocean waste disposal system (OWDS), where he emphasised the tidal regime's interference in the gradient of contaminant concentrations. High concentrations of persistent organic pollutants (POPs) and polycyclic aromatic hydrocarbons (PAHs) are also associated with anthropogenic effects on SSEC (Fontanelle et al. 2019).

The sustainable development goal aims related to the environment, biodiversity and sustainable cities have encountered resource constraints and ineffective government actions (Shibata et al. 2015; WHO 2017; UN-HABITAT 2018). Insufficient urban land tenure regularisation in RMBS cities corroborates VN's ‘invisible’ growth and exerts negative impacts on transforming the urban environment and public health in SSEC waters and sediments. It is of great complexity to study a natural phenomenon that intensifies due to anthropic activities’ interference in coastal environments, especially those that cause eutrophication. The potentially harmful impact portrays this complexity, avoiding an alarmist attitude. We cannot avoid this phenomenon, but we must minimise its causes for maintaining tourism, fishing and improving public health.

Sixty-five percent of the area (Baixada Santista) is occupied by areas of permanent environmental preservation (APPs) with mangroves, restingas and forests in rugged mountains (https://www.diariodolitoral.com.br/cotidiano/baixada-tem646-do-territory-in-preservation-area/122420/). Permanent environmental preservation is defined by the Brazilian Forest Code (Law No. 12,651 of May 25, 2012) as untouchable areas, where it is not allowed to build, cultivate or economically exploit. For it to exist, it is enough that the geographical condition is met, regardless of the domain of the existing area or vegetation. The limits of the areas of permanent environmental preservation (APPs), which should be strictly monitored, are, in practice, abandoned as a result of the scrapping policy of the inspection bodies (Oliveira et al. 2020). The result is constant invasions, rapidly increasing the vulnerable population and causing conflicts between public institutions, where investments by the concessionaires in infrastructure works are prevented by legal uncertainty, resulting from the condition of a permanent preservation area. Therefore, it is necessary to change the current environmental management system so as to allow human activities integrated with the responsibility of maintaining processes, phenomena and riverside resources. In other words, we must encourage the concession of riverside resources within management plans with guidelines and responsibilities to conserve water and the environment.

The geometric rate of annual growth of the population in non-conforming housing (GAGR_NH) is approximately five times higher than that of the compliant population in the Baixada Santista Metropolitan Region (BSMR). It exceeds all world growth rates, even in the poorest regions of Latin America and sub-Saharan and West Africa.

The vulnerable nuclei (VN) growth clusters show that 85% of the VN result from invasions, reinvasions, densification and verticalisation, while 15% represent the government's areas’ demobilisation actions, without actions to recover degraded areas.

The release of sewage in the Santos and São Vicente Estuarine Complex (SSEC) by the study area group (SAG) exceeds 450 tonnes · month⁻¹ and a flow of 2,650,000 m³ · month⁻¹, and the negative impacts from the release and disposal of waste on the banks of water bodies pose risks to public health.

Estuary hydrodynamics do not promote the renewal of SSEC waters and turn its water into a large receptacle for sewage and emerging pollutants. As this is a port region, the contamination of these water bodies has potential risks of contamination and the spreading of diseases worldwide.

A comparison of these historical data clearly shows the escalation of nutrient entry into SSEC and increased concentrations associated with the growth of informal populations in the Santos metropolitan region beyond the limit of the estuarine system's carrying capacity, revealing the enormous pressure on the ecosystem.

The results show accelerated degradation of ecosystems, damage to public and environmental health, and potential risks of spreading disease in SSEC.

The re-urbanisation of the area using economic resources caused by the loss of water must be taken to reduce the risks of ecosystem degradation, damage to health and the spread of diseases.

This study has great potential to solve problems of urbanisation and sanitation in slum areas using resources from the economy generated by non-waste of treated water in irregular distribution. In a global scenario, this proposal could also be used in other regions of irregular housing in Brazil, and even studies of this nature in other parts of the world in less developed countries can lead to similar results and, consequently, solve water contamination problems.