Assessment of Groundwater Contamination in the Southeastern Coast of Brazil: A Potential Threat to Human Health in Marica Municipality

: Groundwater pollution is a current issue that may result in considerable negative effects on human health and the ecological balance. In the present study, the authors evaluated pollutants in groundwater in Maric á Municipality, located on the east side of Rio de Janeiro state in Brazil. The evaluated parameters were temperature, pH, electrical conductivity, Eh, dissolved oxygen, chlorides, nitrates, dissolved organic carbon, total inorganic carbon, phosphates, and total and thermotolerant coliforms. Due to the large number of evaluated points, they were divided into zones according to the respective hydrographic basin. The local accelerated urbanization accompanying income from oil production has led to uncontrolled population growth and associated groundwater pollution. The results of the present study suggest that sewage pollution of Maric á groundwater is already a signiﬁcant issue. The lack of investment in basic sanitation has led to an imbalance in the local groundwater reservoir. In certain locations of the municipality, dissolved organic carbon (DOC), nutrient, and bacteria concentrations increase and spread in the aquifers because of domestic waste disposal. As aquifers are the main source of freshwater for the residents, contamination of them represents a potential threat to local public health.


Introduction
Groundwater is the largest global source of freshwater, representing a fundamental reservoir for humanity that is exploited for domestic, agricultural, and industrial purposes [1].About 30% of the Earth's population uses groundwater as drinking water [2].It is especially essential in arid and semi-arid areas, where rain is scarce and there are few surface water reserves [3].Preserving an unpolluted and renewable source of groundwater for human demands represents one of the biggest challenges of sustainable development for every country [4].This is even more important in the present scenario of global warming and the consequent rise in sea levels, which may result in the salinization of several subterranean water reservoirs located in coastal regions [5].Additionally, uncontrolled human occupation and agglomeration, excessive urbanization, agricultural and industrial activities, and uncontrolled water exploitation all negatively impact groundwater quality and availability [6].
Groundwater contamination due to organic pollutants such as hydrocarbons and pesticides and inorganic substances like heavy metals, microplastics, and endocrine disruptors poses a substantial threat to human health [7,8].During the last three decades, several authors have considered the chemical pollution of groundwater [6,[9][10][11][12][13].Although the major pollutants are of geologic origin, resulting from dissolution of the aquifer rock within the Earth's crust [14][15][16], the recent increase in the world's population has led to increases in anthropogenic contaminants.The most impacted areas are those that are experiencing rapid economic development [17][18][19].Several researchers have focused on the impact of megacities on groundwater [20,21], but few scientists have evaluated small coastal cities, where urbanization has recently intensified.
The Brazilian coastal area currently comprises 40% of the country's total population.Although some coastal cities in Brazil have moderate groundwater demand, the constant population increase tends to intensify groundwater exploitation [22].Because of the recent discovery of the huge petroleum reservoir in the oceanic pre-salt layer and oil production expansion, certain Brazilian municipalities located on the southeast coastal zones have benefited from fees charged by the oil extraction industry and are now facing new social and environmental impacts [23].One of the main results is exponential migration and the resulting increase in population accompanying new job opportunities.This has occurred in the coastal city of Maricá.
The present study provides a diagnosis and spatial groundwater chemical and microbiological characterization of wells from sedimentary and fissured aquifers in this recently urbanized coastal area.It discusses contamination and salinization of aquifers, identifying patterns that may be occurring in many recently urbanized coastal regions in Brazil.One of the main objectives of the present study is, through the assessment of groundwater quality in the coastal municipality of Maricá, to inquire about whether the royalty payments from the oil industry to these municipalities have helped mitigate secondary socio-environmental impacts arising from oil production or whether these same payments have generated new problems, particularly in water quality, due to the local population increase resulting from the pursuit of new income opportunities.

Study Site
Maricá is a municipality of the Rio de Janeiro metropolitan area, located on the Atlantic coast.Its geology is marked by the presence of metamorphic, igneous, and sedimentary rocks, with great geodiversity.It includes the Jaconé beachrocks, whose sedimentary formations were described by Darwin and are considered natural heritage of high geological, environmental, landscape, and cultural relevance.
The coastal geomorphology of Maricá presents an ecologically important lagoonal system, composed of four main lagoons and two sandy barriers that isolate the coastal system from the adjacent sea.Its sedimentary history, architecture, and evolution took place in the Quaternary.It is composed of six lithological units forming three sedimentary sequences compartmented by erosive surfaces [24].As for the geological aspects, the coast located to the west of the Cabo Frio point undergoes a sudden inflection, having an east-west alignment, and is called the Coastal Cords coast [21].In structural terms, it is part of a geological complex composed predominantly of granite and gneiss, represented in the landscape by coastal massifs.
The aquifers found in the area are of the granular type, comprising heterogeneous alluvial deposits and portions of soil and weathered rock.Alluvial sediments are composed predominantly of quartz sands and, subordinately, silty and clayey soils, which occur in the vicinity of the lagoons.These are due to the formation of the coastal lowland during the last transgression and regression movements in the Holocene, between 5000 and 7000 years ago.The coastal lowland is formed by lateral variations parallel to the coastline, with sandy highs and low vegetation typical of restinga and sandy-clay wetlands.These make up the marshes and mangroves in the region.The underground water horizon level is generally near the soil surface, at depths from a few centimeters to a few meters.In the area of the sands, which corresponds to the shallowest places, the water is generally less brackish than in the swampy lowlands [25].The municipality has groundwater as its main source of freshwater.With the growing demand for water resources underground, supply and contamination problems are expected, in addition to the phenomenon of seawater intrusion in these aquifers.The groundwater resource in the target area has been suffering degradation in its quality in response to the advance of the marine saline wedge, brought about by excessive uncontrolled pumping and organic pollution [25].

Methodology
A total of 124 groundwater samples were collected through pre-installed wells already in use by the population in the plain area of the Maricá Basin (Figure 1) during the winter season.The points were divided into nine zones with different urban occupation degrees and with different hydrographic basins.All of the groundwater samples were kept in a portable refrigerator and transported back to the lab at 4 • C to be analyzed within one week.Chemical examination of the groundwater included determination of the temperature, pH, electrical conductivity, Eh, turbidity, dissolved oxygen, dissolved solids, chlorides, nitrates, dissolved organic carbon, dissolved inorganic carbon, phosphates, and total and thermotolerant coliforms.Proper sampling techniques and handling were used to produce high-quality data.Brown glass sampling bottles, which had been previously cleaned with deionized water, underwent a triple rinse with water collected from each sampling location before being used for sampling.Each rinsing cycle utilized a volume of 2.5 L. Subsequently, these bottles were transported to the laboratory within 24 h for preliminary processing.The water samples were analyzed in accordance with the testing procedures outlined in the Groundwater Quality Standard (GB/T 14848-2017 [26]).
water is generally less brackish than in the swampy lowlands [25].The municipality h groundwater as its main source of freshwater.With the growing demand for water r sources underground, supply and contamination problems are expected, in addition the phenomenon of seawater intrusion in these aquifers.The groundwater resource in th target area has been suffering degradation in its quality in response to the advance of th marine saline wedge, brought about by excessive uncontrolled pumping and organic po lution [25].

Methodology
A total of 124 groundwater samples were collected through pre-installed wells a ready in use by the population in the plain area of the Maricá Basin (Figure 1) during th winter season.The points were divided into nine zones with different urban occupatio degrees and with different hydrographic basins.All of the groundwater samples we kept in a portable refrigerator and transported back to the lab at 4 °C to be analyzed with one week.Chemical examination of the groundwater included determination of the tem perature, pH, electrical conductivity, Eh, turbidity, dissolved oxygen, dissolved solid chlorides, nitrates, dissolved organic carbon, dissolved inorganic carbon, phosphates, an total and thermotolerant coliforms.Proper sampling techniques and handling were use to produce high-quality data.Brown glass sampling bottles, which had been previous cleaned with deionized water, underwent a triple rinse with water collected from eac sampling location before being used for sampling.Each rinsing cycle utilized a volume 2.5 L. Subsequently, these bottles were transported to the laboratory within 24 h for pr liminary processing.The water samples were analyzed in accordance with the testing pr cedures outlined in the Groundwater Quality Standard (GB/T 14848-2017 [26]).The first five parameters (temperature, pH, electrical conductivity, Eh, dissolved oxygen) were measured in situ using a multiparameter Horiba U10 probe.The chloride analysis used back titration with potassium thiocyanate.Dissolved organic carbon (DOC) was determined via the method defined by Van Hall et al. [27].Interferences from particulate carbon and inorganic carbon were removed before analysis via filtration through glass fiber filters and sparging with CO 2 -free gas after acidification of the sample [28].Phosphate and nitrate were analyzed via colorimetric methods.
To determine bacterial levels, water samples were plated on mFC (membrane fecal coliform agar) and typical colonies identified as E. coli with EC-MUG (Escherichia colimethylumbelliferyl-β-D-glucuronide) medium.The 124 samples obtained during the present study were also evaluated directly for E. coli through modified mTEC (membrane thermotolerant Escherichia coli) agar [29].
Data for all parameters were tested for homoscedasticity and normality before being submitted to one-way ANOVA (variance analyses) to test whether there was a statistical difference between the zones.The Tukey test was used to compare average values when necessary.Pearson's correlation analysis was performed between the total coliform data and the other parameters.All statistical analyses were performed using the GraphPrism 8.0 software (GraphPad Software-v.10.0.3), accepting 5% variation as significant.

Results and Discussion
The chemical constitution of groundwater is directly influenced by the composition of the water percolating the soil, as well as the resulting by-products and kinetically controlled reactions within the aquifer basin and overlying subsoil coverage [30].As a universal solvent, water mobilizes minerals from the soil and bedrock with which it comes into contact.The physicochemical characteristics of drinking water, on the other hand (temperature, pH, dissolved oxygen levels, conductivity, turbidity, organic matter and NH3, potential contaminants and other chemical constituents), eventually impact its portability, in some cases influencing consumers' health, possibly as a result of the survival of harmful microorganisms [31].
Surface water temperature controls the metabolism of the aquatic ecosystem.For instance, relatively high water temperatures may reduce its ability to hold essential dissolved gasses like oxygen, potentially killing fish and other water organisms [32].Variations in groundwater temperature may trigger changes in biogeochemical mechanisms in the subsurface environment, impacting water quality [33,34].Laboratory assays allow for the identification of processes like carbonate precipitation, silicate dissolution, mobilization of cations, trace elements, and dissolved organic carbon (DOC) [35][36][37][38][39].In the present study, the temperature values varied between 21.5 and 29.61 • C, with one anomalous record of 35.1 • C (average of 24.83 • C).Opportunistic pathogens, including Legionella spp., can grow in the water systems in buildings, representing a critical public health issue [40,41].According to World Health Organization, water temperature is important for the control of Legionella spp., and water temperatures should be maintained above 50 • C to prevent the growth of this organism [42].
PH represents one of the main physicochemical parameters influencing the behavior of water-quality parameters as well as pollutant concentrations in aquatic ecosystems [43].This parameter also influences the communities of bacteria and other microorganisms.In general, relatively high or low pH conditions can make water improper for certain purposes.At higher pH levels, metals tend to precipitate, whereas other compounds like ammonia become toxic to aquatic life, releasing bad odors and tastes [44].At lower pH levels, heavy metals tend to dissolve, becoming bioavailable, and chemicals like cyanide and sulfide become more toxic.The pH values determined in the present study are presented in Table 1.
Of the 124 sampling stations, 47 showed pH values in disagreement with Brazilian legislation, which represents almost 38% of the monitored points.Every zone had at least two sampling stations presenting values above the minimum allowed by the Brazilian law CONAMA 357/05.It is important to emphasize that the minimum pH value in zone 02 (3.11) is alarming.This value is close to the pH for solutions such as vinegar and orange juice.Additionally, five other sampling stations in zone 02 recorded pH values below 5.00.There was no statistically significant difference in pH values among the zones (p > 0.05).The U.S. Environmental Protection Agency and the equivalent Arabian legislation suggest that the pH of water sources should be maintained at between 6.5 and 8.5.According to Nasseem et al. (2022), it is better to have greater alkalinity, below 7.0, in human drinking water, since it keeps the water safe for drinking.According to the same authors, acidic water with a pH of less than 6.5 suggests potential contamination with pollutants, making it unsafe for drinking purposes.Additionally, water with a pH < 6.5 could be corrosive, leaching metal ions such as Fe, Mn, Cu, Pb, Ni, Cr, and Zi from the aquifer rocks or transporting piping nets [6].Throughout the present study, water pH values were more acidic than those acceptable by the legislation, varying at around 6.04, and several times being below 6.In fact, 81 sampling stations (approximately 65%) showed unacceptable pH values.
Dissolved oxygen (DO) levels have a direct impact on groundwater quality by regulating the valence state of heavy metals and the microbial catabolism of dissolved organic compounds [45].A decrease in dissolved oxygen levels can result in anaerobic patterns, which negatively impacts aquatic organisms.The organic matter potentially released from surface sources through a groundwater reserve, on the other hand, can rapidly decrease the dissolved oxygen in the groundwater, turning it into a reducing underground environment more susceptible to the dissolution of the Fe and Mn that compose the aquifer rocks [46].The Brazilian law CONAMA 357/05 suggests a minimum dissolved oxygen concentration of drinking water of 6.00 mg•L −1 .In the present study, the recorded oxygen levels (Figure 2) suggest a high oxygen demand in some zones.Zones 05 and 07 showed DO concentrations of 4.21 and 4.93 mg•L −1 , respectively.On the other hand, the other seven zones did not suggest a high oxygen demand, with DO concentrations varying at around 6 mg/L.When we compared the DO concentration of zones 05 and 07 with that in zone 08, we found a statistically significant difference between them.
The dissolved organic carbon (DOC) sometimes showed high concentrations, especially in the most urbanized zones.The DOC averages varied.All zones had at least two collection points whose values exceeded the CONAMA 357/05 limit of 10 mg•L −1 .Only one zone (zone 03) had an average value above the maximum allowed by law.Approximately 35% of all sampled stations (43 points of all zones) had values above the limits allowed by CONAMA 357/05.Zones 05, 06, 07, and 03 were those with the highest proportion of points above this limit.The summary of the DOC values is shown in Table 2.
The potability of groundwater is directly linked to DOC concentrations, which influence water chemistry and microbial levels [47][48][49][50][51].As a result, there have been several studies on the concentrations, sources, and diffusion of natural DOC in aquifers [52][53][54]; however, to date, few have focused on human health.DOC consists of the carbon part of dissolved organic matter (DOM), typically representing more than 90% of the whole organic carbon content in natural groundwater reserves [55].Nevertheless, levels above background concentrations may indicate organic pollution [48,54,56].The dissolved organic carbon (DOC) sometimes showed high concentrations, especially in the most urbanized zones.The DOC averages varied.All zones had at least two collection points whose values exceeded the CONAMA 357/05 limit of 10 mg•L−1.Only one zone (zone 03) had an average value above the maximum allowed by law.Approximately 35% of all sampled stations (43 points of all zones) had values above the limits allowed by CONAMA 357/05.Zones 05, 06, 07, and 03 were those with the highest proportion of points above this limit.The summary of the DOC values is shown in Table 2.The potability of groundwater is directly linked to DOC concentrations, which influence water chemistry and microbial levels [47][48][49][50][51].As a result, there have been several studies on the concentrations, sources, and diffusion of natural DOC in aquifers [52][53][54]; however, to date, few have focused on human health.DOC consists of the carbon part of dissolved organic matter (DOM), typically representing more than 90% of the whole organic carbon content in natural groundwater reserves [55].Nevertheless, levels above  Comparing the results of the present study with the Canadian legislation for untreated drinking water (4 mg•L −1 of DOC), we observed that the percentage of points above the allowed value increased to 53.22%, which corresponds to 66 sampling stations.This means that more than half of the water wells would be in unfit condition for consumption according to Canadian legislation.
High concentrations of DOC in water may result in aesthetic and odor problems, in addition to the potential stimulation of pathogenic bacteria [57][58][59].High DOC levels also result in a significant impact on the geochemical dynamic of other pollutants, such as pesticides, pathogens, and pharmaceuticals; lower oxygen conditions may decrease the degradation of carbon-based compounds [60].High levels of COD in groundwater may also suggest the development of trihalomethanes in water disinfected with active chlorine.When compared to other environments, the values obtained in the present study were significantly high (Table 3).In a way similar to that of other substances, chloride in groundwater originates from both geogenic and anthropogenic sources.In the second case, agricultural, industrial, and/or domestic wastes are considered potential causes [69,70].Chloride concentrations in uncontaminated waters often stay below 10 mg•L −1 and sometimes below 1 mg•L −1 .On the other hand, high levels of chlorides are suggestive of pollution [71].Although they may be present in most freshwater ecosystems, large concentrations are potentially toxic to freshwater organisms.The results are shown in Table 4.The by-products of chlorine disinfection potentially affect consumers' health.Their magnitude is influenced by a number of variables, such as period of action, levels, and frequency of exposure.Compared to other locations, the studied area revealed extremely high values.The results found in this study ranged between 11.5 and 1466.2 mg•L −1 .The U.S. Environmental Protection Agency (EPA) and the Brazilian legislation recommend a maximum value of 250 mg•L −1 for drinking water.In the present study, several sampling stations recorded values significantly higher than that.Chloride compounds have two main natural sources: soil chloride dissolved during water runoff and seawater intrusion during high tides.An addition of 1% seawater can increase the chloride content to 190 mg•L −1 [72].Anthropogenic chloride sources are mainly industrial wastewater discharge in densely occupied areas; industrial wastewater and domestic sewage represent significant sources of chloride in water bodies.In the present study, chloride values varied between 1472.4 and 11.5 mg•L −1 (average 154 mg•L −1 ).Aside from the potential health threats related to high blood pressure, these chloride concentration limits have been established to protect water from tasting salty and to prevent a corrosive effect on plumbing.
Nitrogen and phosphorus levels may indicate wastewater contamination and can be a threat to human health.Excessive levels of nitrate may cause disease.High levels of nitrate in drinking water may decrease blood oxygen transport, resulting in health issues such as blue baby syndrome [73,74].According to the China Bureau of Quality and Technical Supervision, the acceptable limits of nitrate for drinking groundwater is 20.0 mg•L −1 [3].In the present study, all values of nitrate remained below these values.Brazilian CONAMA 357 legislation limits the nitrate concentration in drinking water to 10 mg•L −1 .
The nitrate concentration found in the present study ranged from 0.00 to 27.98 mg•L −1 .Zones 04, 05, and 07 showed 100% of their collection stations, in accordance with CONAMA 357.All zones yielded mean and median values below the maximum allowed by Brazilian law.However, zones 08 and 09 had the highest proportion of points in disagreement, with approximately 15% being above the Brazilian law limits.A summary of the nitrate values can be found in Table 5.Although the findings for nitrate concentrations were relatively positive, the total organic nitrogen concentration (TON) presented a slightly more worrying scenario.As for nitrate, zone 05 presented 100% of its collection points with TON concentrations in accordance with CONAMA 357.However, zone 09 had the highest average TON, as well as the point with the highest overall concentration (36.23 mg•L −1 ).Zones 01 and 08 also showed average values above the legal maximum.A total of 50% of the points in Zone 08 had TON concentrations above the legal limit.The ANOVA showed a statistical difference between zone 03 and zones 08 and 09, with zones 08 and 09 presenting TON means significantly higher than that of zone 03 (p < 0.05).The same results were observed for zones 05, 08, and 09, with zones 08 and 09 presenting TON means significantly higher than that of zone 05 (p < 0.05).There was no difference between the other studied areas.Figure 3 presents the statistical analysis across all zones, and Table 6 shows the summary of the TON information for all areas studied.presents the statistical analysis across all zones, and Table 6 shows the summary of the TON information for all areas studied.Phosphorus is a fundamental element for all living beings.However, excessively elevated phosphorus levels can result in eutrophication of surface water.Groundwater, on the other hand, can be an important diffuse source of phosphorus to surface aquatic environments.It is generally accepted that phosphate groundwater concentrations are negligible due to high rates of adsorption to the soil and sediment matrix.In the present study, recorded values of phosphate varied between 2.32 mg•L −1 and the detection limit (<0.01 mg•L −1 ).The phosphorus concentrations indicated excess phosphorus, with at least 40% of the collection points of all zones being in disagreement with CONAMA 357 (Table 7).Approximately 69% of all zones had values above the CONAMA 357 maximum of 0.02 mg•L −1 .The ANOVA showed a statistical difference between zones 01 and 02 and zone 07 (Figure 4), with zone 07 presenting a mean phosphorus concentration that was significantly higher than those of zones 01 and 02 (p < 0.05).Phosphorus is a fundamental element for all living beings.However, excessively elevated phosphorus levels can result in eutrophication of surface water.Groundwater, on the other hand, can be an important diffuse source of phosphorus to surface aquatic environments.It is generally accepted that phosphate groundwater concentrations are negligible due to high rates of adsorption to the soil and sediment matrix.In the present study, recorded values of phosphate varied between 2.32 mg•L −1 and the detection limit (<0.01 mg•L −1 ).The phosphorus concentrations indicated excess phosphorus, with at least 40% of the collection points of all zones being in disagreement with CONAMA 357 (Table 7).Approximately 69% of all zones had values above the CONAMA 357 maximum of 0.02 mg•L −1 .The ANOVA showed a statistical difference between zones 01 and 02 and zone 07 (Figure 4), with zone 07 presenting a mean phosphorus concentration that was significantly higher than those of zones 01 and 02 (p < 0.05).
Eng 2023, 4, FOR PEER REVIEW 10  Most pathogenic microorganisms found in water are of fecal origin and are spread via fecal-oral exposure.These pathogenic agents can produce relatively mild gastrointes-  Most pathogenic microorganisms found in water are of fecal origin and are spread via fecal-oral exposure.These pathogenic agents can produce relatively mild gastrointestinal disorders or serious disease such as infectious hepatitis, encephalitis, and myocarditis.Thus, the negative impacts resulting from the consumption of contaminated water on human health can range from low-level infections (mild diarrhea) lasting a few days to critical illnesses that require medical care or even hospitalization, potentially culminating in death [75].Fecal coliforms constitute a group of relatively harmless microorganisms present in the intestinal tract of warm-and cold-blooded animals that are also involved in the digestive process [76].Of these, Esterichia coli is the most common representative and indicates that the water is polluted with fecal material from humans or other animals [77].
On the other hand, the mere presence of these organisms, although harmless, may indicate that the water may have been contaminated by pathogenic organisms or diseasecausing bacteria or viruses, which may also exist in fecal material.Runoff is the main carrier mechanism of pathogen transport to surface water bodies.During a rainfall event, the water distribution between surface runoff and soil percolation results from many factors: storm water flux and extension, soil physical features (e.g., porosity and permeability), land height gradients, and soil vegetal or urban cover [78].If rainfall load exceeds the capacity of the soil to absorb water, overland flux occurs, and microorganisms can be transported in surface runoff [79,80].
The results found in the present study suggest significant important contamination of the groundwater with some source of industrial or, mainly, domestic sewage.Brazilian legislation allows the presence of up to 200 MPN (most probable number) of fecal coliforms in water.In the present study only zone 05 did not showed no collection points with values above the legal limit.However, even at concentrations within the permitted limit, all points in zone 05 showed the presence of fecal coliform cells, which suggests contamination with domestic sewage of the groundwater in that zone, even if small.At least 13% of the collected points of the other zones had coliform concentrations above 200 MPN; for example, 4 of the 29 monitoring stations in zone 02 had values above the Brazilian limit.Although in a relatively low proportion (compared to the other zones), the most worrying factor in zone 02 is the presence of highly contaminated samples, with concentrations up to 12 times higher (2400 MPN) than allowed by Brazilian legislation.
The other zones presented a critical scenario, with the proportion of contaminated points ranging from 35.29 to 83.33%.The minimum average value in these zones (01, 03, 04, 06, 07, 08, and 09) was 218 MPN, which is already above the maximum allowed by Brazilian legislation.The worrying maximum average value was 1455 MPN, found in zone 06.In addition to this worrying average, it is important to note that 83.33% of the sampled sites in zone 06 had contamination above the permitted level, further aggravating the magnitude of the problem in that area.Another important fact is that, of all 124 points analyzed, only 7 showed no presence of coliforms.With the exception of zone 05, all other zones had at least 1one point with at least four times more total coliforms than allowed by law.Table 8 presents the summary of the results found for total coliforms in all zones.Pathogens are released from sewage in the soil; however, most of them remain associated with the fecal deposit.The amount depends on a number of factors, such as the source, age, type, and pathogen level in the fecal matter itself, as well as the survival characteristics of the pathogens.Pathogen survival in water depends on many factors, including water quality (e.g., turbidity, dissolved oxygen, pH, organic matter content) and environmental conditions (e.g., temperature, predation by zooplankton).Exposure to UV light is a key factor in bacterial, viral, and protozoan die-off in surface waters [78,81,82].An aquifer environment also protects pathogens against UV exposure and facilitates their survival in groundwater.E. coli and fecal enterococci (FE) counts were suggested in some sampling sites.The results of the present study show a strong and positive correlation (p < 0.05) between total coliforms and the concentration of DOC, TON, and phosphorus in groundwater, corroborating possible contamination with domestic sewage.Figure 5 shows the three correlations.
Eng 2023, 4, FOR PEER REVIEW 12 sampling sites.The results of the present study show a strong and positive correlation (p < 0.05) between total coliforms and the concentration of DOC, TON, and phosphorus in groundwater, corroborating possible contamination with domestic sewage.Figure 5 shows the three correlations.

Conclusions
Availability of groundwater of good quality is essential for the maintenance of human and animal health, especially in areas with scarce freshwater reservoir availability.This necessary quality can be ensured by regular monitoring and protection of water sources against potential contamination.In the present study, quality evaluation based on the chemical composition of groundwater revealed that the required level of some parameters for human health required by the legislation used around the world is not being met.None of the monitored points had the minimum quality required by Brazilian legislation;

Conclusions
Availability of groundwater of good quality is essential for the maintenance of human and animal health, especially in areas with scarce freshwater reservoir availability.This necessary quality can be ensured by regular monitoring and protection of water sources against potential contamination.In the present study, quality evaluation based on the chemical composition of groundwater revealed that the required level of some parameters for human health required by the legislation used around the world is not being met.None of the monitored points had the minimum quality required by Brazilian legislation; all points had at least one parameter in excess.The results of organic matter and fecal coliform evaluations suggest that one of the main sources of pollutants is domestic sewage resulting from a lack of basic sanitation.Additionally, with the exponential population growth observed in the municipality of Maricá and its plans for agro-industrial development, it is expected that the already established conditions will deteriorate significantly, with pollutants of a more recalcitrant and, therefore, more toxic nature being disseminated in the environment.Urgent measures of basic sanitation must be implemented, even before the implementation of an industrial park, as planned by the municipal government, to prevent even more severe impacts from being detected in the near future.
Although only one collection campaign was carried out, it was performed in the winter, when an improvement in groundwater quality is expected.The quality of the local water would be even worse in the summer, when the most intense rains promote greater transport of pollutants to the subterranean compartment.
Groundwater pollution represents a real danger to human communities.There is a great opportunity for the global scientific community to improve existing aquifer management, highlighting its importance to decision-makers and allowing them to understand how we can defend or rescue both the quality and the quantity of these essential resources.Institutional Review Board Statement: The Institutional Review Board Statement is not applicable to this study, as it does not involve human or animal testing.

Informed Consent Statement:
The Informed Consent Statement is not applicable to this study, as it does not involve human or animal testing.

Figure 1 .
Figure 1.Study site and sampling stations in the 9 pre-determined zones.

Figure 1 .
Figure 1.Study site and sampling stations in the 9 pre-determined zones.

Figure 2 .
Figure 2. Dissolved oxygen (mg•L−1) of all nine zones.The values are shown as mean ± SD.Different letters show statistically significant differences between the zones (p < 0.05).

Figure 2 .
Figure 2. Dissolved oxygen (mg•L −1 ) of all nine zones.The values are shown as mean ± SD.Different letters show statistically significant differences between the zones (p < 0.05).

Figure 3 .
Figure 3.Total organic nitrogen (mg•L −1 ) of all nine zones.The values are shown as mean ± SD.Different letters indicate significant statistical differences between the zones (p < 0.05).The horizontal dotted line shows the maximum limit per Brazilian legislation.

Figure 3 .
Figure 3.Total organic nitrogen (mg•L −1 ) of all nine zones.The values are shown as mean ± SD.Different letters indicate significant statistical differences between the zones (p < 0.05).The horizontal dotted line shows the maximum limit per Brazilian legislation.

Figure 4 .
Figure 4. Phosphorus concentration (mg•L−1) of all nine zones.The values are shown as mean ± SD.Different letters indicate significant statistical differences between the zones (p < 0.05).The horizontal dotted line shows the maximum limit per Brazilian legislation.

Figure 4 .
Figure 4. Phosphorus concentration (mg•L −1 ) of all nine zones.The values are shown as mean ± SD.Different letters indicate significant statistical differences between the zones (p < 0.05).The horizontal dotted line shows the maximum limit per Brazilian legislation.

Figure 5 .
Figure 5. Pearson correlation coefficients between total coliforms and DOC (A), TON (B), and phosphorus (C) for all nine zones.The vertical dotted line shows the maximum limit per Brazilian legislation for total coliforms (200 MPN).The horizontal dotted line shows the maximum limit per Brazilian legislation for DOC, TON, and P.

Figure 5 .
Figure 5. Pearson correlation coefficients between total coliforms and DOC (A), TON (B), and phosphorus (C) for all nine zones.The vertical dotted line shows the maximum limit per Brazilian legislation for total coliforms (200 MPN).The horizontal dotted line shows the maximum limit per Brazilian legislation for DOC, TON, and P.
Author Contributions: M.C.M.P.: experiment execution, analysis, and literature review.J.F.D.: experiment execution, analysis, literature review, and writing.B.S.P.: analysis, literature review, and writing.L.d.S.L.: analysis, literature review, and writing.C.C.G.: literature review, English review, and writing.J.A.B.N.: literature review and writing.C.V.N.: analysis and literature review.E.M.F.: supervisor researcher, literature review, and writing.All authors have read and agreed to the published version of the manuscript.Funding: This research was funded by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Companhia de Desenvolvimento de Maricá (CODEMAR).

Table 1 .
Summary of the pH values of all areas sampled.

Table 2 .
Summary of the DOC values of all areas sampled.

Table 2 .
Summary of the DOC values of all areas sampled.

Table 3 .
Groundwater dissolved organic carbon obtained in different studies.

Table 4 .
Summary of the chloride values of all areas sampled.

Table 5 .
Summary of the nitrate values of all areas sampled.

Table 6 .
Summary of the TON values of all areas.

Table 6 .
Summary of the TON values of all areas.

Table 7 .
Summary of the phosphorus concentrations of all areas sampled.

Table 7 .
Summary of the phosphorus concentrations of all areas sampled.

Table 8 .
Summary of the total coliform concentrations of all areas sampled.