Heavy metals concentration in sediment of Makassar Strait

The concentration of heavy metals (HMs) camium (Cd), cuprum (Cu), chromium (Cr), nickel (Ni), lead (Pb), and zinc (Zn) in sediments of Makassar Strait was investigated. We collected sediment samples from 28 research stations. Atomic Absorption Spectrophotometer (AAS) was used to measure HMs in all samples. This research aims to know the levels of HMs’ contamination and pollution in sediments. The analysis revealed that the concentration of all HMs is still low and inlined with the sediment standard guidelines, exception of Cu and Ni. In regards to the value of I_geo and PLI, sediment in the Makassar Strait is still normal for marine life, and sediment is included in unpolluted categories (PLI<1). The sources of HMs in this strait come from human activities in the land of Kalimantan and Sulawesi Island.


Introduction
Makassar Strait is located between the eastern part of Kalimantan Island and the west part of Sulawesi Island. In the coastal areas of the two islands, there are various kinds of activities potentially polluting the marine environment of the region. East Kalimantan, is a very complex estuarine area and is a confluence of several large rivers such as the Mahakam river, Bungus river, Sangata river, Barumuda river, Bungalu river, Karangan river, and Manubar river. Each river has different characters. In addition, East Kalimantan is known as one of the largest foreign exchange earners in Indonesia which has abundant natural resource potential, particularly in the mining and timber sectors. Industry and settlements are growing rapidly along the coast of Sangkulirang-Samarinda. These industries are LNG, coal, organic chemical fertilizers, shipbuilding, iron and steel construction, heavy equipment repair maintenance, tire retreading industry, and wood industry along the Mahakam River. Likewise with the western part of Sulawesi Island, various activities dump waste into the sea waters, thus, it affects the condition of the Makassar Strait waters. Studies on HMs' pollution have escalated in recent decades on a relatively large scale, especially in coastal areas [1]. This is because information on pollution is still very limited in tropical and subtropical areas such as Indonesia, where a large number of heavy metal pollutants come from nature and from human activities, such as ports, industries, agriculture, and housing around the estuarine which causes the surrounding environment to be polluted.
Sediment serves as a heavy metal adsorber which is important in the hydrological cycle. HMs emissions generally come from human activities that accumulate in river or sea sediments, these heavy metals are adsorbed by fine materials like clays. Therefore, sediments can detach HMs to the water layer through anthropogenic or natural processes, and can also have harmful effects on the ecosystem.
The purpose of the study is to determine the level of contamination and to assess the contamination of HMs Cadmium (Cd), Cuprum (Cu), Chromium (Cr), Nickel (Ni), Lead (Pb), and Zinc (Zn) in sediments in the Makassar Strait by considering the Sediment Quality Guidelines, and computing Contamination Factors (CF), Pollution Load Index (PLI), Geoaccumulation Index (I_geo) as well.

Research sites
The research was conducted in the sea waters of the Makassar Strait from September to October 2004 using the RV Baruna Jaya VIII. The position of the station was determined purposively following the research objectives ( Figure 1).

Sampling and Analysis
We used a gravity core to collect the sediment from bottom of the sea then we kept them into a cleaned polyethylene box. We dried the sample using an oven at 105 °C for 24 hours. To get a complete cleaning of the sample, we rewashed the dried sampled with distilled water. The samples wer re-dried using the same heating protocol as previous step till they obtained a constant weight. We ground the samples to gain a fine particle. Those fine samples, 5 grams for each sample, were then underwent a digestion protocol using HNO3/HCl. First step of digestion is to let the mixture in room temperature for at least 4 hours. The second step was heating the mixture at 90 °C for 8 hours [5]. The quantification of Cadmium (Cd), Cuprum (Cu), Chromium (Cr), Nickel (Ni), Lead (Pb), and Zinc (Zn) of the pre-treated/digested samples was carried out using AAS Varian Techtron model IBQ AA-1475.The quality of data was ensured by analyzing a reference material PACS-2. The recovery varied from 95% to 100% and the deviation of reference material's measurement is <5%. The concentration of HMs is expressed in part per million, ppm (dry weight).

Determination of Sediment Pollution Level
The pollution of HMs in sediments was assessed applying several indices for sediment standards such as PLI and I_geo [6][7][8][9][10] as the following formula:

Results
The measurements results of HMs levels in sediments at the Makassar Strait (Table 2 and Figure 2).  From the table above, it can be seen that the levels of Cadmium (Cd), Cuprum (Cu), Chromium (Cr), Nickel (Ni), Lead (Pb), and Zinc (Zn) were diverged at each station. On average, the highest heavy metal content is Zn> Ni> Cr> Cu> Pb> Cd.

Distribution of HMs
The distribution of Pb metal at each station is uneven (Table 2). Overall, Pb levels ranged from 5.32-19.11 ppm with an average of 11.178 ppm. The highest and lowest Pb content was found at station 7 and station 1, respectively. This data shows some stations accumulate greater lead compared to others. The enrichment of metal lead in sediments can come from anthropogenic sources or geological weathering.
The average Pb levels from these observations were relatively high, Edward (2010;2011) reported that Pb levels in sediments in Elat waters (Southeast Maluku) were relatively unpolluted and still natural, ranging from <0.004-0.274 ppm with a mean of 0.042 ppm [11,12]. Other locations also dhowed unpolluted water by Pb such as in Ngilngof, Tual (Southeast Maluku) 3.187-3.921 ppm, and in Ohoimas (Southeast Maluku) 2.781-4.033. This Pb level is still lower than the normal Pb level found in nature, which is 12.5 ppm [13]. The Canadian Council of Ministers of the Environment (CCME, 2002) assigns 35 ppm as the threshold value of lead in sediments for the protection of biota [14]. Meanwhile, the Sediment Quality Guidelines (SQG) assigns Pb content of <40 ppm as the uncontaminated sediment [13,15]. KMNLH (2010) determined the Pb Threshold Value in sediments for biota to be 36.8 ppm [16]. Based on the CCME, SQG, and KMNLH criteria above the Pb level are still safe for marine biota that lives and forages in sediments Cd levels in the sediment ranged from 0.02-0.035 ppm with an average of 0.158 ppm. Cd levels are also not evenly distributed at each station. One station showed the highest levels of Cd (station 6) and two stations (26 and 27) exhibited the lowest concentration. Station 6 was suspected to receive more Cd input than others. Cd levels in these three locations were relatively low. Edward (2010;2011) found Cd levels in Elat waters (Southeast Maluku) which were relatively unpolluted and still natural ranged <0.001-0.0172 ppm (mean= 0.009 ppm), in Ohoimas (Southeast Maluku) 0.216-0.295 ppm  [11,12]. The CCME (2002) decides 0,6 ppm as the threshold value of cadmium in sediments for the protection of biota [14]. KMNLH (2010) determined the Cd Threshold Value in sediments for biota to be 6.2 ppm [16]. According to Solomon & Forstner in [17] the level of Cd in the uncontaminated sediment is 0.11 ppm. The average level of normal Cd in nature is 0.2 ppm [13]. Based on the provisions of CCME and KMNLH and still safe for marine life.
Cu content in the sediment ranged from 7.8-33.03 ppm with an average of 18.464 ppm and was not evenly distributed at each station. The highest Cu is found at station 7 and the lowest at station 25. This data shows that station 7 receives more Cu-containing waste input. The Cu levels in the three research locations were relatively high, Edward (2011Edward ( , 2010 reported that Cu levels in Elat waters (Southeast Maluku) were relatively unpolluted and still natural, ranging from <0.015-0.512 ppm (mean 0.067 ppm), in Ohoimas (Maluku Southeast) 0.216-0.295 ppm with an average of 0.251 ppm and in Ngilngof (Southeast Maluku) <0.001-0.029 ppm with an average of 0.039 ppm [11,12]. The CCME (2002) states 35.7 ppm as the threshold value of Cu in sediments for the protection of biota [14]. SQG determine uncontaminated sediments with Cu levels <25 ppm [13,15]. KMNLH (2010) determined the Cu Threshold Value in sediments for biota to be 108 ppm [16]. Thus, referring to CCME and KMNLH above, it can be said that the sediment in these two waters is still normal for marine life.
Cr content in the sediment ranged from 12.07-43.04 ppm with an average of 25.386 ppm and uneven at each station. The highest and lowest Cr content is found at station 21 and station 1, respectively. This data shows that station 21 receives Cr input greater than other stations. Normal Cr content in nature is 100 ppm [18]. The permissible threshold value of Cr in sediments for marine biota is 52.30 ppm. The Sediment Quality Guidelines (SQG) designates Cr content of <25 ppm as uncontaminated sediment [13]. Thus, this Cr content base on CCME is still safe for marine life.
Zn concentration in the sediment ranged from 36.24-103.03 ppm with an average of 70.324 ppm. Zn levels also vary from station to station. The highest Zn level is found at station 22 and the lowest at station1. Zn levels are still relatively low when compared to natural levels of Zn in nature, namely 70 ppm [13]. Edward (2011Edward ( , 2010 reported that Zn concentration in Elat waters is relatively unpolluted and unspoiled, ranging from 0.008-0,361 ppm with an average of 0.067 ppm, in Ohoimas between 0.294-2.834 ppm with an average of 0.888 ppm and Ngilngof between 0.43-36.85 ppm with an average of 14.39 ppm [11,12]. The CCME (2002) designate 123 ppm as the threshold value of Zn in sediments for biota protection [14]. KMNLH (2010) determined threshold value of Zn in sediments is 271 ppm [15]. SQG determine that sediments that are not polluted by Zn have Zn levels <90 ppm [13]. Thus, when referring to CCME, KMNLH, and SQG, Zn levels in the sediment are still safe for the life of the biota.
Ni concentration ranged from 12.8-43.29 ppm with an average of 27,213 ppm. Ni concentration also varies at each station. The highest and lowest Ni content is found at station 19 and station 1, respectively. Station 19 received more input of waste containing Ni. The Ni content in this study was relatively high. Edward (2010) found Ni concentration in the waters of Ohoimas Southeast Maluku which were relatively unpolluted and still natural ranged from 0.826 to 1.119 ppm, in Ngilngof between 0.702-1.141 ppm, in North Bangka 1.518-13.831 ppm, East Bangka 3.557-7.562 ppm, South Bangka between 2.473-11.355 ppm [19]. The British Columbia Ministry of Water, Land and Air Protection (BCMWLAP) (2006b) sets 16 ppm as that the lowest value of Ni in sediment causing negative effects [20]. The normal average level of Ni in nature is 75 ppm. The SQG determine the uncontaminated sediments by Ni content is <20 ppm, and 20-50 ppm as moderately polluted sediments [13]. Based on the BCMWLAP, Ni content is dangerous for marine biota.  Table 3. CF Pb value ranges from 0.266-0.955 with a mean of 0.558. The highest Cf Pb value was found at Station 7, namely 1.528, and the lowest was at Station 1, namely 0.425. This data shows that station 7 has a higher level of contamination than other stations. Station 1, 2, 8, 10-19, 23-27 showed Cf value ranges from 0.425-0.992. This value is <1, which means that the stations have a low contamination level, while stations 3-7, 20-22, the Cf value ranges from 1.021-1.528, this value is fell between 1 and 3 (1 <Cf <3) and included in the moderately contaminated category. On average, the level of Pb contamination was <1. The Cu contamination factor value ranged from 0.111 to 0.60 with a mean of 0.263 (<1), which means it was categorized as low contamination. The highest level of contamination was found at station 7 and the lowest at station 5. The value of the Cr contamination factor ranged from 0.127 to 0.430 with a mean of 0.253 (<1) which means it is a low level of contamination.

Contamination Factors (CF) and Pollution Load Index (PLI)
The highest level of Cr contamination was found at station 21 and the lowest at station 1. The value of the Zn contamination level ranged from 0.517 to 1.471 with a mean of 1.022 (<1), which means it is also in the low contamination category. The highest level of Zn contamination was found at station 22 and the lowest at station 1.
The value of the Ni contamination level ranged from 0.17 to 0.577 with a mean of 0.369 (<1), which means it is also in the low contamination category. The highest level of Ni contamination was found at station 19 and the lowest at station 1.
Based on the data above ( Table 2) the mean concentration of contamination are as follows: Zn>Pb>Cd>Ni>Cr>Cu. This shows that Pb has a higher level of contamination than other metals. The overall PLI value varied from 0.227-0.669 (mean 0.413), this value is <1 meaning unpolluted condition in the sediment in these waters, except for station 20. The PLI is 1.1534 (> 1) implying a lightly polluted category.

"Geoaccumulation Index (I_geo)"
The results for the geo accumulation index's calculation are presented in Table 4. The Igeo value of Pb spread from -2.495 to -0.65 (mean of -1.512). The I_geo value of Pb is in the negative range and the mean <0, reflecting unpolluted condition by Pb. The I_geo values of cadmium is ranged from -4.491 to -0.362 with a mean of -1.828. This value means the sediment is unpolluted by Cd (I_geo value < 0). I_geo values of Cu spread between -3.75 and -1.668 (mean= -2.66). The sediment is categorized uncontaminated with Cu (value <0).

Comparison with Sediment Quality Standards (SQG)
In the following table (Table 5), we can see the comparison of HMs concentration in sediments in the Makassar Strait with toxicological reference values and natural concentration (geochemical background) (ppm). From the following table, the average concentration of cadmium, cuprum, chromium, nickel, lead, and zinc is still lower than their natural geochemical concentration. The concentration of cadmium, chromium, lead, and zinc were still per the criteria for toxicological purposes, while Cu and Ni are higher than the TRV and LEL criteria set by the US EPA and the Ontario Ministry of Environment (MOE), but still under the criteria set by the US Department of Energy and Canadian Environment Quality Guideline. When referring to the US EPA and OMOE criteria above, only Cu and Ni metals need to be watched out for.

Correlation between parameters
The pearsons' correlation analysis among metals Pb, Cd, Cu, Cr, Zn, and Ni are presented in Table  6. A positive correlation among metals Pb, Cd, Cu, Zn, Cr, and Ni was computed with a significance level of 1%. The existence of this correlation indicates that the six metals originate from the same source, suspected from human activities on the mainland islands of Kalimantan and Sulawesi Islands. This condition was also found by [17] in the Sulawesi and Sulu Seas, where it received a significant positive correlation among Al, Fe, Mn, Cu, Ni, Co, and Cr metals. Furthermore, Harikumar et al., (2010) also reported a positive correlation among cuprum, nickel, lead, manganese and chromium on the southwest coast of India.