Spatial distribution of total petroleum hydrocarbons in the seawater and sediment of Southeast coast of India

The spatial distribution of total petroleum hydrocarbons (TPH) were analysed in the seawater and sediment samples collected from 27 locations along the Southeast coast of India. A first-time assessment was carried out on the distribution of TPH in both water and sediments for the entire coastline of Tamil Nadu. The concentration of TPH in seawater showed large spatial variation ranging from below detection level (BDL) to 47.5 μg/L and 0.01 to 53.12 μg/L in the surface and bottom waters, respectively. TPH levels exceeded the regulatory limits specified by FAO, China’s Marine Monitoring Standards and the European Community in the seawater samples of Thoothukudi harbour (S2 station). The results showed that seawaters of southern stations were comparatively more polluted with TPH. TPH values in sediment were between 2.33 and 30.07 μg/g, and their levels remained below the Marine Sediment Quality Standard (500 μg/g). The spatial profile of TPH in sediments were contrasting to that observed for seawater. Higher TPH values were observed in sediments of the northern region than southern. TPH contents are strongly correlated with clay (R2 = 0.776; P < 0.001) and silt (R2 = 0.648; P < 0.001); conversely, there is a significant negative correlation between TPH and sand (R2 = 0.753; P < 0.001). ANOVA analysis demonstrated a significant difference (F = 11.75; p < 0.01) between the TPH concentrations of water and sediments. Non-metric multidimensional scaling (nMDS) was performed to determine the similarity among sampling stations that formed five crusted groups. Sediment along the southeast coast can be categorised as slightly polluted with respect to TPH as per the ATSDR standards.


Introduction
The coastal environments receive a huge amount of sewage and industrial waste through rivers and estuaries specially in developing countries (Adeniji et al., 2017;Muthukumar et al., 2013).Petroleum hydrocarbons often contaminate coastal environment through waste discharge from petrochemical industries, harbours, marine traffics and oil spillage (Das & Chandran, 2011).Petroleum hydrocarbons are complex mixtures of aliphatic and aromatic compounds and are major constituents in a variety of commercial products such as gasoline, crude oil, lubricating oils, fuel oils, mineral oils, solvents and mineral spirits.It degrades at a very slow rate and forms one of the pollutants of potential concern in the marine environment (Das & Chandran, 2011;Kostka et al., 2020).Total petroleum hydrocarbon is highly toxic with mutagenic and carcinogenic properties (de Mora et al., 2010;Hallier-Soulier et al., 1996;Masakorala et al., 2013;Nicolaus et al., 2017).Previous studies have reported that petroleum hydrocarbons can be toxic to larvae in the sea even at very low levels (0.1 ppm) (Mazhar et al., 1987;USEPA, 1986).In some cases, death and genetic mutations in marine mammals, shellfish, fish, reptiles and birds occured due to the toxicity of petroleum hydrocarbons (Ansari et al., 2012;Kennish, 1997;Mazhar et al., 1987).Therefore, periodic assessment of TPH in the coastal water and sediment is essential to ensure the safety of the coastal ecosystem.Once petroleum hydrocarbon enters into the coastal water, they gradually settle down to the sediments by getting deposited as layer (0-20 cm) in the bottom sediment (Al-Imarah et al., 2006).The lower molecular weight fraction of petroleum hydrocarbons generally gets removed by evaporation, while the heavier components get dispersed in the water layer.Their accumulation in sediments gets subsequently transferred to biota affecting the benthic organisms, bottom feeders and pose risks to human health through trophic transfer (Chouksey et al., 2004;Hentati et al., 2013).The total petroleum hydrocarbon load to the ocean was estimated to be 2.37 × 10 6 tonnes.y−1 (Kennish, 1997) from different human activity-based sources such as coastal refineries, urban runoff, tanker accidents, operational discharges (oil transportation and shipping sources), air-borne fallout, natural seep and offshore production discharges (GESAMP, 1993).The National Response Centre has recorded the petroleum discharge to the marine environment to be 1.3 million tonnes/year from the identifiable sources (National Response Centre, 2003).The Bay of Bengal coast is highly vulnerable for oil pollution.The major cause being large are oil tankers that are transporting fuel mainly through the southern Bay of Bengal (Sen Gupta et al., 1993;Sharma, 2009).
In the present study, we assessed the spatial profile of TPH covering the south east coast of India (~ 876 km long) of the Indian Peninsula.The Environmental Information System Centre has reported that Tamil Nadu has about 12,000 industries, and out of these, 5500 industries are situated in and around the coastal areas (Ramesh et al., 2008).Coastal activities such as industrial oil discharge, oil exploration, oil refining, ports and harbour, fishing, tourism and recreational activities are responsible for the hydrocarbon pollution along this coast (Ramesh et al., 2008).Previous studies have assessed the TPH pollution in sediment and water at some selected locations (Gurumoorthi & Venkatachalapathy, 2017;Natarajan et al., 2006;Selvaraj et al., 1999;Topgi et al., 1982;Veerasingam et al., 2010;Venkatachalapathy et al., 2010a, b).However, there is no study available yet on the distribution of TPH in both water and sediments for the entire coastline of Tamil Nadu, even though various industrial settlements like factories, oil refineries, ports and fishing harbours along the Tamil Nadu coast are increasing in number.Therefore, it becomes imperative to assess the distribution of total petroleum hydrocarbon in the Tamil Nadu Coast.The main objectives of this study were to assess the distribution of total petroleum hydrocarbon (TPH) in both seawater and sediments of the Tamil Nadu coast, as well as to determine the content of sand, silt, and clay for sediment characterization.The results of this study could serve as comprehensive baseline information on TPH pollution for planning and management to ensure the safety of the coastal ecosystem.

Study area
The Indian coast is divided into two categories, namely, coasts on the western India and coasts of the eastern India.The southern part of the eastern coast of India forms the southeast coast of India, which mostly comprises the coast of Tamil Nadu and Pondicherry states (Ingole, 2005).The Tamil Nadu coastline, situated on the southeast coast of the Indian Peninsula, is a length of 1076 km, establishing it as India's second-longest coastline.Prominent ports like Ennore, Chennai, Thoothukudi, and Nagapattinam are strategically situated along this coastal stretch.Within Tamil Nadu, there exists a substantial industrial presence around 12,000 industries.Among these, approximately 5500 industries are strategically located in and around the coastal regions.Notably, about 1500 industries are situated along the Chennai coast (Ramesh et al., 2008).The primary coastal activities contributing to marine pollution along the Tamil Nadu coast involve the release and disposal of both treated (at a rate of 1.8 million litres per day) and untreated sewage, as well as industrial waste.In addition, heated water discharge from power plants cooling systems, oil spillage, chemical spillage and activities such as oil exploration, oil refining, fishing using mechanized vessels, painting of fishing vessels, draining of waste oil, scrapping of fishing vessels, dumping of wastes and trash fishes, dredging, dumping of ship wastes, cargo handling, recreation, and tourism activities and salt production are equally responsible for coastal pollution in Tamil Nadu (Ramesh et al., 2008).Additionally, Tamil Nadu presently accounts for 15% of India's overall marine catches.There are thirteen significant landing centres for mechanized boats distributed along the extensive 1000 km coastline, accommodating a total of 6012 vessels (Bavinck et al., 2008;Bhathal, 2005).These fishing activities might also lead to petroleum hydrocarbon pollution.
An important feature of the Tamil Nadu coast is the presence of 796 km long Buckingham Canal (part of the National Waterway 4 (NW-4), which originates in the Godavari district of Andhra Pradesh and runs parallel to the coastline up to Villupuram District of Tamil Nadu.In this segment, of the coastal region, the canal opens into the coastal waters at various locations such as Ennore Creek, Cooum river estuary (Chennai), Adyar river estuary (Chennai), Muttukadu Backwaters, Edaiyur Backwaters, Sadras Backwaters, Palar River estuary, Marakanam and Pondicherry.The canal receives untreated sewage and industrial discharge from Chennai and the nearby industrial establishments.

Sample collections and analysis
Surface and bottom seawater and surface sediment samples were collected from 27 ecologically distinct locations along the Tamil Nadu coast (Fig. 1).Samples were collected on-board Coastal Research Vessel Sagar Purvi equipped with all essential equipment.Pre-cleaned (using n-hexane) and oven-dried (50 °C) amber glass bottles were rinsed with ambient seawater before collecting the water samples.Seawater samples from the surface (< 0.5 m) and bottom were collected using a Niskin's water sampler.Physicochemical parameters such as pH, temperature and dissolved oxygen (DO) were measured onboard.Suspended particulate matter (SPM) was calculated as the difference between the initial and final weight of the filter paper after drying at 105 °C overnight.One litre water sample was collected from each location and stored at 4 °C until further analysis.Total petroleum hydrocarbon content in the water was extracted in triplicates with n-hexane by following the standard method (IOC- UNESCO, 1984).The organic phase containing the analytes was separated, dried with anhydrous Na 2 SO 4 and concentrated using a rotary evaporator.The extracts were analysed using a UVfluorescence spectrometer (Hitachi, F-2700).
Sediment samples were collected using Van Veen Grab and stored at 4 °C until further analysis.Samples were air-dried and gently ground by mortar and pestle.Total petroleum hydrocarbon in the sediment was extracted using n-hexane by sonicating the mixture in an ultrasonic bath for 2 h (IOC- UNESCO, 1982;Tam et al., 2005).The supernatant hexane extract was filtered with 0.45-μm filter paper and cleaned with anhydrous Na 2 SO 4 .Total petroleum hydrocarbon content in the concentrated extract was measured by UV fluorescence spectrometer.The total petroleum hydrocarbon contents were quantified as chrysene equivalent based on the emission at 360 nm monitored at 310 nm excitation (MOOPAM, 2005).All samples were analysed for TPH in triplicates, and average values are reported.Samples were spiked with the Chrysene standard to evaluate the percentage recovery of the analytical method.Percentage recoveries for spiked samples were 92-102%, with a precision of 95%.The method detection limit of TPH as chrysene equivalent was 0.01 µg/L and 0.1 µg/g for seawater and sediment, respectively.

Sediment characteristics
About 100 g each of sediment samples were desalinated by washing repeatedly with distilled water, treated with hydrogen peroxide (H 2 O 2 ) to remove organic matter and dried at 50-60 °C.Dried sediment samples were sieved by a mechanical sieve shaker and used for sediment characterization (Buchanan, 1984;Ingram, 1970).Sediment fractions (< 62 µm) were analysed using a Malvern particle size analyser (Mastersizer-2000G) to quantify the distribution of silt and clay (Ramaswamy & Rao, 2006).

Statistical analysis
Statistical analysis was carried out by using SPSS 22 software.One-way ANOVA approach is chosen to gain a deeper understanding of the nuanced variations existing between two different environmental media.In the present study, one-way ANOVA has been used to analyse the TPH in water (surface and bottom) and sediment data to assess the nature of the significant differences between the two environmental media.Non-metric multidimensional scaling (nMDS) was performed using PRIMER 6.1 software to determine the similarity among stations.To understand the resemblance of spatial distribution of TPH concentrations in the studied coast, non-metric multidimensional scaling (nMDS) analysis was performed.nMDS is a rank-based indirect gradient analysis approach in which the actual distance is substituted with ranks to elucidate the spatial interrelationship among a set of data.

Seawater characteristics
The observed values for physicochemical parameters were within the expected range for the seawater in the present study area (Fig. 2a-e).The highest seawater temperature was recorded at S12 (surface water) and lowest was recorded for S27 bottom waters (Fig. 2a).Salinity values (29.88 to 35.78 PSU) were always observed to be higher for surface seawater than bottom water (Fig. 2b).Due to the influence of freshwater discharge from Vaigai River at S6, S7 and S8 and from Muttukadu backwater at S26, salinity values at these stations were observed to be comparatively lower.The hydrogen ion concentration, i.e. pH values varied between 7.40 (lowest for S26) and 8.17 (S18 bottom water) (Fig. 2c).The lowest pH observed at S26 station could be due to the freshwater input from Muttukadu backwaters.The findings of the current study corroborated with previous observations in the Muttukadu coastal region, where salinity and pH values were reported to be consistent (pH 7.40; salinity 31.36 psu) due to the influence of freshwater input (Barath Kumar et al., 2018).DO values varied from 3.60 to 6.82 mg/l in surface waters and for bottom water samples it varied from 2.80 to 6.81 mg/l (Fig. 2d).DO levels in seawater at S27 stations (2.80 mg/L at bottom and 3.60 mg/L at surface) were less than the minimum of 4 mg/L O 2 concentration essential for the survival of aquatic organism.According to China's Seawater Quality Standard (GB3097-1997), the DO values of seawater along the coast complied with the clean (category I) to slightly polluted (category III) category.The seawater at S27 was found to be the most deficient in DO and belonged to the medium polluted (category IV) to highly polluted (category V) category of seawater.S27 station is located close to the Adyar river estuary, which collects a large volume of untreated sewage from Chennai (Jayaprakash et al., 2012;Silambarasan et al., 2012).As a result, the breakdown of organic waste released into coastal waters at this location might have caused the depletion of DO.A previous study by Barath Kumar et al. (2018) also recorded below the minimum of 4 mg/L O 2 (2.80 mg/L) at Pattinapakkam which is located near the Adyar river estuary.According to a study conducted by Mishra et al. (2015), it was revealed that the mouths of the Cooum and Adyar rivers consistently showed the lowest dissolved oxygen levels (0 to 12.37 mg/l).They have recorded hypoxia (< 4 mg/l) at mouth regions during low tide throughout the year.Furthermore, recent research by Begum et al. (2021) has reported even more extreme conditions, with occurrences of anoxia (complete absence of DO) near the Adyar river.It is evidence that S27 is polluted with organic waste from the Chennai megacity through the Adyar and Cooum river estuary.The resulting low DO levels pose significant threats to aquatic life, emphasizing the need for immediate environmental intervention and measures to manage sewage and organic waste disposal to restore the health of the coastal ecosystem.SPM levels exhibited significant variation along the coast, in surface water, SPM ranged from 0.014 to 38 mg/l, whereas it varied between 0.018 and 31 mg/l in the bottom water.SPM concentrations were found to be very low in the water of the northern region of coast (S26 and S27) (Fig. 2e).

Spatial distribution of TPH in surface and bottom seawater
Total petroleum hydrocarbon concentration in the seawater (surface and bottom) and sediment is presented in Fig. 3a-d.The concentrations in the surface and bottom waters ranged between BDL-47.5 μg/L Fig. 1 Sampling stations along Tamil Nadu coast.S1, Thoothukudi harbour; S2, Thoothukudi harbour-2; S3, Vaippar river mouth; S4, Mookaiyur fishing harbour; S5, Valinokkam; S6, Mandapam; S7, Vaigai River mouth; S8, Thiruppalaikudi; S9, Thondi; S10, Kottaipattinam fishing port; S11, Kattumavadi harbour; S12, Mallipattinam; S13, Kodiyakarai-1; S14, Kodiyakarai-2; S15, Kodiyakarai-3; S16, Vedaranyam canal; S17, Nagapattinam; S18, Tharangambadi; S19, Kollidam River mouth; S20, Parangipettai; S21, Cuddalore; S22, Pondicherry; S23, Marakkanam; S24, Near Palar River Mouth; S25, Kalpakkam; S26, Muttukadu; S27, Chennai harbour ◂ 1203 Page 6 of 16 Vol:. ( 1234567890) and 0.01-53.12μg/L, respectively.The total petroleum hydrocarbon content was observed to be often high in the bottom water compared to the surface water.Higher concentrations of TPH were recorded for the water samples collected towards the south end (Thoothukudi) and north end (Chennai) stations, whereas the central coast seems to be unpolluted with respect to TPH (Fig. 3b).The presence of many industries, harbour and intense urban developments in the north and south coast of Tamil Nadu might be responsible for the elevated TPH in the nearby coast.Such kind of anthropogenic influence is relatively less in the central coast of Tamil Nadu.The spatial distribution patterns of TPH indicated that they are mostly from marine-based sources such as harbour activities, ship movements, oil transport, industrial effluents discharge, fishing and ferry activities since accidental oil spills or natural seepages were not reported recently in the southern region of Tamil Nadu.The concentration of TPH observed in the seawater samples from the southern region were higher.Similar high TPH levels were observed in the sediments towards the north.The present and previous studies have shown that southern region of Tamil Nadu coast (Gulf of Mannar coast) is sandy with abundant calcareous debris (Jonathan et al., 2004;Karikalan et al., 2020;Kumar et al., 2013).The northern regions were characterised by mud with the dominance of organic matter from the river.Sandy sediments have lesser efficiency to absorb TPH from the water compared to muddy sediments because the clay, colloidal materials and organic matter in the mud are generally surface-active (Gorleku et al., 2014;Gurumoorthi & Venkatachalapathy, 2017;Massoud et al., 1996;Trapido, 1999).The waves play an important role in vertical mixing and sediment transport.The correlation of textural distribution with TPHs content in the surface sediments along the coast suggested that they were mainly controlled by waves and longshore currents (Kaliraj et al., 2014).High TPH concentration in seawater at S1, S2 and S4 stations in the Gulf of Mannar (GoM) may be attributed to the release of TPH from sediments to the water column by turbulence and mixing because the swells and waves are high in the GoM during the month of January to April (Gowthaman et al., 2013).

Textural characteristics and distribution of TPH in sediment
The textural characteristics of sediment such as sand, silt and clay contents significantly influenced the distribution of TPH and control their partitioning in water and sediment (Szava-Kovats, 2008).The textural characteristics of the collected sediment samples are presented in Fig. 4a.The percentage of the sand fractions at the Tamil Nadu coast varied from 42.60 to 99.80% with a mean value of 76.84%.The highest values of sand were recorded at S1, while a lower value of sand was found at S13.The sand particles were dominant in southern regions compared to the Northern regions of the Tamil Nadu coast due to the northeast monsoon current.The dominance of sand fractions observed at stations S1-S5 located adjacent to Thoothukudi harbour might be due to the establishment of a spit and the construction of a jetty for the port of Thoothukudi to protect the region from the action of currents.The increased sand content indicated the transport of the finer sediments by the currents from the abrasion zone once it reach the coastal zone (Jonathan et al., 2004;Szefer & Skwarzec, 1988).The percentage of silt and clay fraction was found to vary from 0.10 to 50.67% with the mean value of 18.05% (higher percentage at S13; lower at S1&S3) and 0.10 to 15.98% with the mean value of 5.11% (higher percentage at S12 and lower at S1) respectively.Both silt and clay were more dominant in the northern part of the Tamil Nadu coast due to the input of mud and organic matter from rivers such as Palar River, Cooum, Adyar river and Muttukadu backwater (Venkatachalapathy, et al., 2010a, b).Previous studies have also reported that sediments of Chennai harbour, Cooum and Adayar contain high percentages of mud and silt (Venkatachalapathy et al., 2010a, b).
Total petroleum hydrocarbon content in the sediment samples varied from 2.33 to 30.07 μg/g (dry weight) (Fig. 3c, d).The level of TPHs was highest in the sediment at S27 as the location used frequently for movement of fishing boats and excessive shipping activities in Chennai harbour.Discharges of petroleum refinery industries and land-based wastewater are also common in this station.Further, oil spill occurred due to the oil tanker ship accident at Ennore port (near Chennai harbour) in January 2017 which released more than 100 tonnes of heavy fuel oil (Sivagami et al., 2019).Other stations such as S10, S11 and S15 which are located near fishing harbours also showed a high level of TPH in the sediments (Fig. 3d).The high level of TPH in the fishing areas need to be assessed regularly to ensure the safety of habitat and human health risk due to the consumption of edible organism in the catchment (Li et al., 2010).
The results of the non-metric multidimensional scaling (nMDS) analysis demonstrated that the 27 studied stations clustered into five groups and lied within the Euclidean distance of 1.55 (excluding S2).Total petroleum hydrocarbon concentrations in sediment and water showed opposite trend in all five clustered groups (Fig. 5a-c).Group 1 (S1 and S5) was with high TPH levels in seawater, and group 2 to 5 were with high TPH content in the sediment.The group 5 stations were having the highest sediment TPH values ranging from 25.00 to 30.07 μg/g which could be attributed to the fishing boat and harbour activities.One-way ANOVA indicated a significant difference (F = 11.75;p < 0.01) in TPH concentrations of water and sediments with insignificant correlation between surface seawater, R 2 = 0.017, and bottom seawater, R 2 = 0.015.However, the chances of TPH in sediment being released again into the water column may cause secondary pollution (Zhao et al., 2015).The concentrations of TPH in surface water were strongly correlated (R 2 = 0.997) with TPH concentration in the bottom water due to the mixing.

Compliance with guideline limits
As per environmental quality standards, TPH in water samples except at station S2 (bottom water) were below the Grade II quality standard of 50 μg/L and can be regarded as clean water Class I (CSBTS, 1997).However, maximum TPH (S2, 53.12 μg/L) was five times higher than the European Community regulations limit of 10 μg/L (San Sebastián et al., 2001).The seawater in the southern region was more polluted with TPH and might pose risk to living organisms in the seawater.Comparison of TPH (μg/L) levels in the seawater of studied locations (Table 1) indicates that the observed values of TPH in this study are lower than previously reported values for the Tamil Nadu coast (Natarajan et al., 2006).Total petroleum hydrocarbon values reported in the seawater of several other coastal areas in India and other parts of the world are much higher than the values observed during this study (Table 1).Total petroleum hydrocarbon levels in the surface and bottom seawater (Fig. 3a, b) exceeded the guideline levels of 2.5 µg/L (FAO, 1982) in coastal waters samples of S1, S2 and S5 located at the southern region of Gulf of Mannar to Thoothukudi harbour.ATSDR (1999) specifies TPH concentration to be below 10 μg/g for unpolluted environments and estuarine sediments.The average TPH content (13.08 µg/g) in the sediment assessed in the present study along the Tamil Nadu coast exceeded the level (Fig. 3c) 10 μg/g of ATSDR (1999) indicating that these areas are slightly polluted from the major industries, harbour and petroleum-related activities along the coast.Total petroleum hydrocarbon concentration observed in the sediment was much lower than TPH in several of the other studies as compared in Table 1.Total petroleum hydrocarbon values recorded in sediments during this study were lower than that reported for west coast of India (Chouksey et al., 2004).This could be due to the heavy traffic of oil tankers along the Arabian Sea shipping route than in the Bay of Bengal (Veerasingam et al., 2010).The Page 11 of 16 1203 Vol.: (0123456789) concentrations of TPHs recorded in Tamil Nadu coast sediments were comparable (1.88-39.76μg/g) to the previously reported values in the sediments of Chennai Coast (Venkatachalapathy et al., 2010a, b).Further, TPHs content in the sediment reported in earlier studies along Indian coast and other coastal regions were much lower than that observed in the present study.However, present TPH in sediments were much higher than recently reported levels (6.41 μg/g) in Tuticorin coast (Balachandar et al., 2021) (Table 1).However, in the present study, TPH concentrations in the sediment were lower than the Marine Sediment Quality Standard of first-class standard values of 500 μg/g (CSBTS, 2002).3.14-14.59(Gurumoorthi & Venkatachalapathy, 2017) Pulicat Lake, Southeast coast of India 0.28-6.86(Hemalatha et al., 2020) 1203 Page 12 of 16 Vol:. ( 1234567890)

Conclusions
The total petroleum hydrocarbon contamination in the seawater and sediment of ~ 876 km stretch of Tamil Nadu coast was assessed.The concentration of TPH was ranged from BDL to 47.5 μg/L and 0.01 to 53.12 μg/L in the surface and bottom seawaters, respectively, and their levels in few locations of the southern region have exceeded the international regulatory limit.In sediment, the concentrations of TPH varied from 2.33 to 30.07 μg/g and highest levels in the sediment of Chennai harbour due to movement of fishing boats and excessive shipping activities.Concentrations in the sediment showed strong correlation with silt and clay due to their active binding surfaces.Non-metric multidimensional scaling (nMDS) analysis clustered the 27 studied stations into five groups within the Euclidean distance of 1.55.The trend of TPH content in sediment and water were contrasting with each other without any correlation.According to ATSDR, TPH concentration in the sediment of the Tamil Nadu coast can be categorised as slightly polluted.Water of the studied coastal stretch is fairly unpolluted with respect to TPH in comparison with the prescribed regulatory limit by international agencies.However, levels are expected to rise in the near future since coastal areas of Tamil Nadu are growing faster with the addition of new harbours, petroleum refinery industries, oil exploration and other large industries.The present TPH values can serve as the baseline value, and regular monitoring of the TPH level in different components of coastal environment is suggested to ensure the ecological safety in sediment.

Declarations
Ethics approval This manuscript does not contain experimental studies on animals and is not covered under ethical approval.

Fig. 2 a
Fig. 2 a-e Physicochemical parameters of the coastal waters of Tamil Nadu, a temperature, b salinity, c pH, d dissolved oxygen (DO) and e suspended particulate matter (SPM)

Fig. 3
Fig. 3 Spatial distribution of total petroleum hydrocarbons (a values and b stations) with environmental quality standards in water (FAO: Food and Agriculture Organisation permissible limit is 2.5 µg/L) and sediments (c values and d stations) along

Fig. 4
Fig. 4 Correlation analysis for the total petroleum hydrocarbons and components of the sediment texture along the Tamil Nadu coastal sediments.a Percentage distributions of clay, silt, and

Fig. 5
Fig. 5 Non-multidimensional scaling (n-MDS) bubble plot showing similarities and grouping of sampling stations surface water (a), bottom water (b) and sediments (c).The circle indicates that the division of the 5 main groups separated by similarity and bubbles indicates the relative values of TPH for each station of Tamil Nadu coast.The size of the bubbles indicates the level of TPH concentrations during the study ◂

Table 1
Total hydrocarbon petroleum (TPH) in water and sediments in Indian Coast and other coastal regions