Chemosphere 144 (2016) 1319–1326

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Assessing the distribution and human health risk of organochlorine pesticide residues in sediments from selected rivers Ozekeke Ogbeide a,b,∗, Isioma Tongo a,c, Lawrence Ezemonye a,c a

Laboratory for Ecotoxicology and Environmental Forensics, University of Benin, Benin City, Nigeria Department of Environmental Management and Toxicology, Faculty of Life Sciences, University of Benin, Benin City, Nigeria c Department of Animal and Environmental Biology, Faculty of Life Sciences, University of Benin, Benin City, Nigeria b

h i g h l i g h t s

g r a p h i c a l

a b s t r a c t

•

Samples collected from areas of intensive agricultural activities. • Principal Component Analysis reveals fresh application of DDT, α -HCH, γ HCH, β -HCH. • Health risk of DDT, α -HCH, γ -HCH, β -HCH to rural population through non dietary exposures assessed. • Result raises concerns of possible carcinogenicity for infants and young children. • Higher risk of cancer was seen through direct or indirect ingestion of contaminated sediments.

a r t i c l e

i n f o

Article history: Received 1 July 2015 Received in revised form 24 September 2015 Accepted 29 September 2015 Available online 23 October 2015 Handling editor: Andreas Gies Keywords: Human health risk Pesticide Cancer risk Daily intake Sediment

a b s t r a c t Sediment samples from major agricultural producing areas in Edo state Nigeria were analysed for α -HCH, γ -HCH, β -HCH and  DDT with the aim of elucidating contamination profiles, distribution characteristics, carcinogenic and non-carcinogenic risk of these compounds in these regions. Analysis was done using a gas chromatography (GC) equipped with electron capture detector (ECD), while health risk assessment was carried out using the Incremental Lifetime Cancer Risk (ILCR) and the chronic daily intake (CDI). Results showed varying concentrations of α -HCH, γ -HCH, β -HCH and  DDT pesticides in sediment samples with hexachlorocyclohexane ( HCHs) (4.6 μg/g/dw) being the dominant contaminants as it was widely detected in all samples and stations. Source identification revealed that the current levels of HCHs and DDT in sediments were attributed to both historical use and fresh usage of these pesticides. Risk estimates using ILCR and CDI showed that the risk of cancer and non-cancer effects was highest when exposure route was through ingestion. Furthermore, model projections highlights children as high risk population groups for non-dietary exposure to OCPs. These findings suggests the need for increased monitoring programmes, with a wider scope for both currently used pesticides and legacy/banned pesticides. © 2015 Elsevier Ltd. All rights reserved.

1. Introduction ∗ Corresponding author. Laboratory for Ecotoxicology and Environmental Forensics, University of Benin, Benin City, Nigeria. E-mail addresses: [email protected] (O. Ogbeide), isioma.tongo@ uniben.edu (I. Tongo), [email protected] (L. Ezemonye).

http://dx.doi.org/10.1016/j.chemosphere.2015.09.108 0045-6535/© 2015 Elsevier Ltd. All rights reserved.

Pesticides especially organochlorines form an integral part of our society because of its diverse use in several activities including animal husbandry and public health applications

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(Zhou et al., 2006) and despite its benefits, there is a growing concern at local, regional and global levels about possible environmental contamination from the use of agrochemicals, disposal of outdated stocks, containers and packets (Doong et al., 2002b; Sarkar et al., 2008; Upadhi and Wokoma, 2012). Despite the adoption of the international code of conduct on the distribution and use of pesticides (Code of Conduct) (FAO, 2002), the restriction and control of banned/legacy pesticides have proven difficult in many developing countries including Nigeria. This could be attributed to weak regulations on importation and use of dangerous chemicals, and the inactivity or absence of control agencies at the international borders (Tijani, 2006). This scenario has led to the wanton proliferation of banned chemicals in local markets located in agricultural areas, making large quantities of pesticides available to rural farmers, which eventually could pose potential threats to the environment and health of the people (Williamson, 2003; PAN AP, 2010). In addition, these products are sold without proper training of farmers on safe application and without warning of the harmful effect on the environment (Nwilene et al., 2011). Furthermore, significant proportion of OCPs, typically ranging from 20 to 70% of a pesticide or its degradation products, have been documented to be retained in soils and eventually sediments following application, making sediments the sink for pesticides (Miglioranza et al., 2003; Ezemonye et al., 2008a). In Nigeria, pesticide usage has soared in past decades with at least 21 different documented types of organophosphates, organochlorines and carbamates insecticides available in the market to boost agricultural production and combat disease vectors of plants, animals and humans (Taiwo et al., 2012). As such large quantities of these pesticides are released into the environment in the course of controlling agricultural pests, insect-borne diseases, and termites (Eqani et al., 2009). Concentrations of pesticide residues in the Nigerian environment have been reported by several researchers. Ize-Iyamu et al. (2007), reported high concentrations of OCPs in water, sediment and fish from some rivers in Edo State, while Ezemonye et al. (2008a,b; 2009), studied the pesticide (γ -HCH, endosulfan and propoxur) contamination of water, sediment and two important fish species from Warri River in Delta State. Similarly, Okeniyia et al. (2009), in a study on the distribution of persistent organic pollutants in water samples collected from different rivers in Kaduna, Niger, Benue, Kwara and Kogi States of Northern Nigeria, reported high concentrations of OCPs, while Adeboyejo et al. (2011), Adeyemi et al. (2011) and Williams, (2013a,b) have all reported varying concentrations of OCPs residues in water, sediment and biota from various sections of the Lagos lagoon. Concentrations of pesticide residues observed in these studies were of concern because they were above the recommended limits while sediments samples were found to have the higher concentration of pesticide residues, signalling its role as a sink for pollutants in aquatic systems. In the light of this, there is the need for constant monitoring of pesticide residues in sediments in order to protect Nigeria’s fresh water bodies and its resources. From the public health safety perspective, estimating human health risk that may arise from exposure to organic chemicals is imperative. As such, health risk assessment should predict the probable effects of pollutants in human beings over a specified period (Huang et al., 2014). A few studies including; Jiang et al. (2005); Darko and Akoto (2008); Fianko et al. (2011); Yohannes et al. (2013); Andoh et al. (2013) and Ezemonye et al. (2015) have estimated the potential risk to human health that could arise from the consumption of pesticide contaminated food (dietary intake). However, there is the need to estimate the risk to human health through non dietary exposures. These risks are predicted by some risk assessment models which include the chronic daily intake (CDI) (Huang et al., 2014) and the incremental lifetime cancer risk

(ILCR) (Qu et al., 2014). Considering the dearth of information on the availability of this class of contaminants in the Nigerian environment and the paucity of data to safely predict health risks, this study was designed to profile the composition and distribution of α -HCH, γ -HCH, β -HCH and DDT residues in sediments obtained from three rivers that drain agricultural communities in Edo State and establish public health risk.

2. Methodology 2.1. Site description Sampling sites were chosen from three regions of intense agricultural activities (Fig. 1). Illushi River, drains the Illushi community (N: 06° 39 59.8 ; E: 006° 36 34.2 ). The region is a prominent rice-cultivating lowland area. The surrounding areas of the Illushi River are characterized by intensive rice farming. The Ogbesse River drains the Ogbesse community (N: 06° 45 3.7 ; E: 005° 34 03.2 ). This community is located within the forest belt ecological zone of Edo State. It is prominent for cocoa, plantain and pepper production. The surrounding area of this river is typified by the presence of commercial cocoa farms, which constantly make use of agrochemicals to enhance their production. The Owan River drains the Owan community (N: 06° 45 40 ; E: 005° 46 07.4 ). This town is located in the derived savannah ecological zone of Edo State, Nigeria. Surrounding the river are vast farming areas. The region is notable for its intensive cocoa and plantain production and other types of crop farming. It’s worthy to note that for each of these sites, farms were located by river banks and were constantly/regularly inundated by overflows from each river. 2.2. Sample collection Sediment samples (n = 216) were collected from each river using methods described by Ezemonye et al. (2008a,b). Samples were taken from the positions where an accumulation of fine-texture substrate took place. The upper 2 cm of bed sediment at each site were collected with a teflon-coated spoon and wrapped in aluminium foil. Samples were collected for 18 months. 2.3. Sample extraction and clean up Sediment samples were extracted according to the method described by Hladik and McWayne (2012). A solvent mix (dichloromethane (DCM) and N-hexane) was prepared for the extraction of pesticide residues. 15 g of sediment samples were dried for 48 h and hand sieved through a 2-mm sieve to obtain homogeneous particles. Fine samples were mixed with the solvent mix (dichloromethane (DCM) and N-hexane) and placed in the sonicator and sonicated for about 20–25 min at about 50 °C. A florisil solid phase extraction (SPE) method was used to clean up the extracts (USEPA, 2007). 2.4. Pesticide analysis The cleaned up extracts were analysed for α -HCH, γ -HCH, β HCH and  DDT (4,4 -DDT). Corresponding results were obtained based on the method described by USEPA (2007), using a Hewlett– Packard (hp) 5890 Series II equipped with 63 Ni electron capture detector (ECD) of activity 15 mCi with an auto sampler. The chromatographic separation was done using a VF-5 ms of 30 mm capillary column with 0.25 mm internal diameter and 0.25 μm film

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Fig. 1. Map of Edo State showing various sampling sites.

thicknesses and equipped with 1 m retention gap (0.53 mm, deactivated). The GC conditions were as follows: The oven temperature programme: Initial temperature was set at 60 ° C for 2 min and ramped at 25 ° C/min to 300 ° C for 5 min and allowed to stay for 15 min giving a total run time of 58 min. The injector setting was a pulsed spit less mode with a temperature of 250 ° C at a standard pressure. The injection volume was 1.5 μL. The detector temperature was 320 °C (held for 5 min), Helium was used as a carrier gas while Nitrogen gas (N2 ) was used as the makeup gas, maintained at a constant flow rate of 5 ml/min. The efficiency of the analytical method (the extraction and clean-up methods) was determined by recoveries of an internal standard. The recovery of observed pesticides was greater than 85%, while method detection limit (MDL) for each pesticide was 0.01 μg/g/dw. Peak identifications were conducted by comparing the retention time of standards and those obtained from the extracts. 2.5. Health risk assessment models Humans are exposed to contaminants including pesticides in sediments through several pathways or routes. Notable among such pathways are direct or indirect ingestion of substrate particles; dermal absorption of trace elements in particles adhered to exposed skin; and inhalation of re-suspended particles emitted from sediment through the mouth and nose (Qu et al., 2014). In consideration of the fact that several exposure parameters, such as body weight, ingestion rate, and inhalation rate, changed with age growth, the cancer risk and non-cancer risk were categorized and estimated for two age groups: childhood (0–10 years.), and adulthood (19–70 years). 2.5.1. Chronic daily intake (CDI) Chronic daily intake is a model, designed by USEPA, (1992 and 1997) to estimate the non-carcinogenic risks for adults and children from non-dietary exposure to contaminants. CDIs are estimated for exposure through ingestion, inhalation and dermal contact. The CDI was estimated using the following formulae adapted

from Huang et al., 2014. (Equations (1)–(3)).

CDIingestion =

(1)

C(sediment ) × (1/PEF ) × IAR × EF × ED BWxAT

(2)

C(sediment ) × SA × CF × EF × ED × ABS × AF BWxAT

(3)

CDIinhalation =

CDIdermal =

C(sediment ) × IR(sediment ) × CF × EF × ED BWxAT

Where CS is the concentration of pesticides in sediment samples, ingestion rate (sediment) (IR) is 200 (mg/d) for children and 100 (mg/d) for adults; exposure frequency (EF) is 350 (d/yrs); exposure duration (ED) is 6 years for children and 30 years for adults; body weight (BW) is 10 and 30 kg for children and adults respectively; average life span (AT) is 2190 D for children and 8760 D for adults; surface area (SA) is 2800 cm2 /d for children and 5700 cm2 /d for adults; dermal surface factor (AF) 0.2 mg/cm and 0.07 mg/cm for children and adults respectively; inhalation rate (IAR) (air) is 10.9 m3 /d for children and 17.5 m3 /d for adults; particle emission factor (PET) is 1.36E+09 m3 /kg for children and 1.36E+09 m3 /kg for adults. A conversion factor (CF ) of 1 × 10−6 was used for CDI estimates. (USDOE (2011), Qu et al. (2014), Ezemonye et al. (2015), Huang et al. (2014), USEPA (2002)).

2.5.2. The incremental lifetime cancer risk (ILCR) The incremental lifetime cancer risk (ILCR) represents the incremental probability that an individual will develop cancer during his lifetime as a result of exposure to a potential chemical carcinogen (Chiang et al., 2009; Qu et al., 2014). ILCR of dermal, inhalation and ingestion pathways in this study was calculated using the following equations adapted from the USEPA standard models (Qu et al., 2014). (Equations (4)–(6)). The carcinogenic slope factors of OCPs are obtained from the Integrated Risk Information System (IRIS).

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CS × CSF ingestion ×

ILCRsingestion =

 (BW/70 ) × IRsed × ED × EF (4)

BWxATxCF



ILCRsdermal =

 3

CS × CSF dermal ×

 3

 (BW/70 ) × SA × F E × ABS × AF × EF × ED (5)

BWxATxCF



ILCRsinhalation =

CS × CSF inhalation ×

 3

 (BW/70 ) × IRair × ED × EF (6)

BWxATxCF

Where CS is the concentration of pesticides in sediment samples, ingestion rate (sediment) (IR) is 200 (mg/d) for children and 100 (mg/d) for adults; exposure frequency (EF) is 350 (d/yrs); exposure duration (ED) is 6 years for children and 30 years for adults; body weight (BW) is 10 and 30 kg for children and adults respectively; average life span (AT) is 2190 D for children and 8760 D for adults; surface area (SA) is 2800 cm2 /d for children and 5700 cm2 /d for adults; dermal exposure ratio (FE) is 0.61; dermal surface factor (AF) 0.2 mg/cm and 0.07 mg/cm for children and adults respectively; dermal absorption factor (ABS) is 0.13; inhalation rate (IAR) (air) is 10.9 m3 /d for children and 17.5 m3 /d for adults; particle emission factor (PET) is 1.36E+09 m3 /kg for children and 1.36E+09 m3 /kg for adults. A conversion factor (CF ) of 1 × 106 was used for ILCRs estimates. (USDOE (2011), Qu et al. (2014), Ezemonye et al. (2015), Huang et al. (2014), USEPA (2002)).

3. Results and discussion 3.1. Spatial distribution of HCH and its isomers Pesticide analysis showed varying concentrations of α , β and γ Hexachlorocyclohexane (HCH) in sediment samples (Table 1, Figs. 2 and 3). Concentration of each isomer of HCH in sediment samples were in the following order β -HCH > α -HCH > γ -HCH. Distribution of HCHs in the various agro-ecological region in this study, shows that the Illushi region had higher concentrations of β -HCH while the Ogbesse region had the highest concentration of γ -HCH and the Owan region had the highest concentration of α -HCH. This implies that HCH has been utilized for agricultural activities within these communities. After application, residues of HCH are transported into nearby rivers that serve as drains for commercial agricultural farms. Technical HCH, a relatively cheap and readily available insecticide, contains four principal isomers isomers; α -HCH (65–70%), β -HCH (5–6%), γ -HCH (13%), and δ -HCH (6%) with γ – HCH being the only effective insecticide (Li et al., 1998). However in this study, the average composition of HCH isiomers measured in sediment samples were β -HCH (39.44%), α -HCH (41.11%) and γ -HCH (19.45%), which suggests that there was a recent input of technical HCH and much of the γ -HCH is converted to α -HCH. Its been reported that α -HCH is very unstable and converted to β -

HCH in the environment, thus the dominance of α -isomer in sediment samples reflects the recent use of technical HCH (Kannan et al., 1995). Further indicators of contaminant source age, were also determined using the ratio of α -HCH/γ -HCH (Calamari et al., 1991). Generally, the ratio of α -HCH/γ -HCH is between 3 and 7 in technical HCH and is 0 in lindane. If there is no application of technical HCH over a period of time, the ratio of α -HCH/γ -HCH will be larger than 7; yet, if there is new input of γ -HCH (lindane), the ratio will be below 3 (Chen et al., 2011). As observed in this study, the average ratio of α -HCH/γ -HCH was below 3, an indication of the recent use of γ -HCH (Lindane). However, the average ratio of β -HCH/γ -HCH in investigated sediment samples was 2.02. This implies that occurrence of HCH was also from historical application and trace pollution sources (Wang et al., 2007). The ratios of α -HCH/γ -HCH and β -HCH/γ -HCH in sediment samples of selected rivers in Edo state, reveals that the occurrence of HCH was both from fresh input of γ -HCH (Lindane) and historical applications of technical HCH. This trend corroborates the findings of Wang et al. (2007), Olatunbosun et al. (2011), Doong et al. (2002a) and Chen et al. (2009) who reported high concentrations of various isomers of HCH in sediment samples.

3.2. Spatial distribution of DDT The concentration of dichlorodiphenyltrichloroethane (4,4 DDT), ranged from 0 (ND) to 6.1 ug/kg/dw (Fig. 3) and was lower than  HCH concentrations in sediment samples. Further observations revealed that the Ogbesse River, had the highest concentration of  DDT when compared with the Illushi and Owan Rivers. Several factors might be responsible for the presence of  DDT at varying concentrations in sediment samples from Edo state: fresh input of DDT; its slow degradation from historical use; and its environmental persistence (Hu et al., 2009). DDT has been reported as one of the most persistent and durable of all insecticides because of its insolubility in water and very low vapour pressure (Hoffman et al., 2003). There has been reports in Nigeria of the current use of DDT in the control of malaria vector (Ovuorie, 2013), with DDT intended for malaria vector control, diverted for agricultural activities despite existing prohibitions.

Table 1 Concentration (μg/g/dw) of HCH and DDT in sediment samples from rivers in Edo State. Illushi

α -HCH γ -HCH β -HCH  HCHs  DDT

Ogbesse

Owan

Total mean

Mean

±SD

Range

Mean

±SD

Range

Mean

±SD

Range

1.52 1.20 2.17 4.89 0.97

1.01 2.11 1.90 3.28 1.36

ND-3.8 ND-8.45 ND-6.1 ND-6.6 ND-6.1

1.26 1.65 2.03 4.08 1.16

0.36 0.64 0.19 1.14 0.28

ND-5.1 ND-6.1 ND-5.85 ND-6.5 ND-4.35

2.13 1.10 1.67 4.90 0.93

1.68 1.60 1.51 3.39 1.49

ND-5.5 ND-4.55 ND-4.85 ND-5.25 ND-4.85

1.64 1.32 1.96 4.62 1.02

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Fig. 2. Concentration of α -HCH and γ -HCH in sediment samples.

3.3. Total concentration of pesticide residues in sediment samples

3.4. Principal component analysis

Total OCPs in sediment samples ranged from ND- 8.45 μg/g/dw. It was also observed that β -HCH (1.96 μg/g/dw), had the highest total mean concentration followed by α -HCH (1.64 μg/g/dw), γ -HCH (1.32 μg/g/dw) and 4,4 -DDT (1.02 μg/g/dw). Furthermore, the presence of OCPs in sediment samples indicates the contamination of rivers through the prolonged application of pesticides for farming. This implies that a large proportion of pesticide residues that enters into these rivers binds to suspended particles and settles at the bottom of the river, leading to a compromise in the sediment quality of each river studied. Similar studies have also reported heavy contamination of sediments by OCPs (Aktar et al., 2009; Olatunbosun et al., 2011; Hellar-Kihampa, 2013). High concentration of OCPs observed in sediments could be attributed to the chemical and physical properties of each pesticide which allows for high sorption interactions in sediment samples (Hu et al., 2009). Concentrations of  DDT and  HCH observed in this study varied from one river to another and this could be attributed to the differences in physicochemical properties of sediments from each river. Sediment physiochemistry has been reported to influence the distribution and availability of organochlorine pesticides (Bhattacharya et al., 2003; Idowu et al., 2013).

Observed pesticide residues concentration in sediments was subjected to principal component analysis (PCA) in other to determine their possible origin/sources and degradation behaviour. 79.5% of the total data variance could be explained by three principal components. PC 1 accounted for 43% of the total variance and was highly associated with high positive loadings for β -HCH, γ HCH and  DDT. This implies that β -HCH and γ -HCH in the investigated sediments have a similar degradation pattern, with both isomers being the product of the degradation of α -HCH. Results also shows that both isomers have a common source of origin which is technical HCH (Hu et al., 2009; Qu et al., 2014). PC2 accounted for 23% of the total variance and was positively loaded for α -HCH. There was also a negative correlation with β -HCH, γ -HCH, confirming that its presence in the environment was from fresh inputs of technical HCH. This is because α -HCH is a very unstable isomer of HCH and is readily converted to a more stable isomer β -HCH.

Fig. 3. Concentration of β -HCH and 4,4 DDT in sediment samples.

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Table 2 Comparison of pesticides levels (μg/g/dw) with other parts of the world. Rivers

Country/region

 HCHs

 DDT

Reference

Illushi Ogbesse Owan Calabar river Bakassi river Imo river Oginni river Ovwian Warri river Ekakpamre Warri river Agboi Creek, Lagos Lagoon Tarkwa Bay, Lagos Lagoon Ogba river Ovia river Ikoro river Bohai sea Peacock river, China Qiantang river, China Suzhou river, China Lake Burullus, Egypt Taiwan rivers Cameron Highlands FSSB ERL

Nigeria Nigeria Nigeria Nigeria Nigeria Nigeria Nigeria Nigeria Nigeria Nigeria Nigeria Nigeria Nigeria Nigeria China China China China Egypt Taiwan Malaysia

4.89 5.22 4.90 0.01 0.02 0.01 0.07 11.48 4.82 0.209 0.0199 0.713 0.79 0.6 0.0008 0.0014 0.037 0.00411 0.031 1.03 0.00806 6

0.97 0.85 0.93 0.29 0.0049 0.0059 0.037 NA NA 0.139 0.012 0.733 0.56 ND 0.0014 0.00055 0.021 0.0147 0.071 0.39 0.0065 4.2 3

This study This study This study Olatunbosun et al. (2011) Olatunbosun et al. (2011) Olatunbosun et al. (2011) Olatunbosun et al. (2011) Ezemonye et al. (2008b) Ezemonye et al. (2008b) Williams, (2013a) Williams, (2013b) Ize-Iyamu et al. (2007) Ize-Iyamu et al. (2007) Ize-Iyamu et al. (2007) Hu et al., 2009 Zhou et al., 2006 Hu et al., 2005 Said et al., 2008 Doong et al., 2002a,b Saadati et al., 2012 USEPA, 2006 Long and McDonald, 1995

NA: Not available. FSSB: Freshwater sediment screening benchmark. ERL: Effect Range Low.

3.5. Comparison of pesticides levels (μg/g/dw) in sediments in this study with other relevant studies Concentrations observed in this study were significantly higher in comparison to concentrations observed in studies by Ize-Iyamu et al. (2007); Olatunbosun et al. (2011); Williams (2013a,b) in Nigeria as presented in Table 2. However, mean concentrations of  HCH and  DDT in sediments observed in this study were lower than concentrations reported by Ezemonye et al. (2008a) and Okoya et al. (2013) in sediments from some rivers in Delta and Ondo states respectively. Compared with other regions of the world, the mean concentration of  HCH and  DDT in sediment was significantly higher than those in sediments from other areas (Table 2). This observation is quite worrisome, owing to the toxic potentials of HCH and DDT in the environment. The high pesticide residual concentrations in sediments observed in this study, could be attributed to the fact that these pesticides are still in use illegally within these regions in attempt to ensure high agricultural productivity. Furthermore, Reports have also stated that these pesticides are illegally used by inhabitants in these regions for indoor spraying, to combat mosquitoes.

3.6. Ecological risk assessment To illustrate the potential ecological risk of  HCH and  DDT in sediment samples, concentrations observed in this study were compared with related sediment quality guidelines (Table 2). For this study, fresh water sediment screening benchmark (FSSB) as proposed by USEPA 2006 and effects range low (ERL) were used. Comparison showed that  HCH and  DDT concentrations were below the FSSB values, while  DDT concentration observed in sediments were lower than ERL. These results indicates that there is no potential risk to sediment dwelling organisms as a result of exposure to observed pesticide concentrations in contaminated sediments.

3.7. Human health risk assessment Human health risk was estimated using ingestion of contaminated sediment, direct contact with skin and inhalation of dust from sediments as routes of human exposure to pesticides. 3.7.1. Incremental lifetime cancer risk (ILCRs) As a means of estimating the integrated life time cancer risks of exposure to sediment-borne OCPs through the pathways of ingesting, dermal contact and inhalation, the ILCR was calculated. Chen and Liao (2006) reports that in most regulatory programs, an ILCR between 10−6 and 10−4 denotes potential risk, while an ILCR larger than 10−4 indicates potentially high health risk. An ILCR of 10−6 or less denotes virtual safety (Chen and Liao, 2006; Peng et al., 2011; Wang et al., 2011; Huang et al., 2014). As seen in Table 3, ILCRs estimates for adults and children through ingestion (direct intake of sediments via putting fingers or hands into the mouth) of contaminated sediments showed cancer risk as estimates ranged from 10−4 to 10−6 , (Qu et al., 2014). Similarly, ILCRs for dermal exposures showed cancer risk because ILCRs estimates ranged from 10−6 and 10−4. However, ILCRs estimates for exposures through inhalation ranged from 10−7 to 1011 which implies that there is no potential cancer risk to humans upon exposure. Further observations showed that ILCRs estimates for α -HCH, γ -HCH, β -HCH and  DDT, where higher in children compared to adults when exposure routes was through ingestion, indicating an increased cancer Table 3 Estimated incremental lifetime cancer risk (ILCRs) for OCPs. Ingestion

α -HCH γ -HCH β -HCH  DDT a

Dermal

Inhalation

Children

Adults

Children

Adults

Children

Adults

3.30E-05a 7.58E-06a 8.13E-06a 1.11E-06a

2.06E-05a 4.74E-06a 5.08E-06a 6.93E-07

5.22E-06a 1.85E-06a 1.86E-06a 3.52E-07

1.33E-05a 4.71E-06a 4.74E-06a 8.96E-07

1.32E-09 3.04E-10 4.66E-10 4.44E-11

1.65E-09 3.8E-10 5.83E-10 5.56E-11

Indicates potential cancer risk.

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Table 4 Estimated chronic daily intake (CDI) compared with reference dose for OCPs. Ingestion

α -HCH γ -HCH β -HCH  DDT

Dermal

Inhalation

Reference dose

Children

Adults

Children

Adults

Children

Adults

3.14E-05 2.53E-05 3.75E-05 1.96E-05

2.80E-06 2.25E-06 3.35E-06 1.75E-06

1.14E-05 9.19E-06 1.37E-05 7.12E-06

4.15E-06 3.34E-06 4.97E-06 2.59E-06

1.26E-09 1.01E-09 1.50E-09 7.84E-10

3.61E-10 2.90E-10 4.31E-10 2.25E-10

risk for children than adults. Results obtained from this study agrees with studies by Qu et al., 2014; who reported potential cancer risk to humans upon exposure to organochlorine pesticides through non-dietary routes. Qu et al., 2014 also reported that risk of cancer was highest through ingestion of contaminated soils and minimal when exposure routes was through inhalation. 3.7.2. Chronic daily intake (CDI) Chronic daily intake (CDI) or non-carcinogenic risk estimated for each pesticide were below their respective reference dose. According to the USEPA’s standards, when the estimated CDI for a contaminant is more than the reference dose (RfD) of the contaminant via each exposure route, the contaminant level would exert an adverse human health effect or non-carcinogenic effect (Huang et al., 2014). Hence for this study, there is no risk of non-cancer effects upon exposure to contaminated sediments. However CDI estimates for each pesticides showed that children where at greater risk compared to adults (Table 4). It was also observed that risk of health effects under non-dietary exposure to organochlorine pesticides increased in the following order: β -HCH > α -HCH > γ -HCH >  DDT. 4. Conclusion The pesticide profile of our environment has become a major concern and this study presents further evidence of this increasing trend. α -HCH, β -HCH, γ -HCH and DDT were observed at varying concentrations in sediment samples from rivers in Edo State, while source determination and degradation pattern of each pesticides showed that present contamination levels were both from historical/accumulated use and current use of these pesticides. Although pesticide concentrations were below standard sediment quality guidelines, it was observed that there could be the possibility of cancer risk through human exposure to contaminated sediments. Using incremental lifetime cancer risk (ILCRs), it was observed that human exposure through ingestion and skin contact could lead to cancer risk in children and adults. However, estimated chronic daily intake (CDI) via ingestion, dermal and inhalation were below the reference dose for each pesticide, indicating these contaminants, under non-dietary intake do not constitute non-carcinogenic health effects. Furthermore, model projections highlights children as high risk population for nondietary exposure to OCPs. These findings suggests the need for increased monitoring programmes, with a wider scope for both currently used pesticides and legacy/banned pesticides. Acknowledgement This study was supported in part by grants-in-aid for scientific research from the Ministry of Education, Culture, Sports, Science, and Technology of Japan, which was awarded to Professor M. Ishizuka (No. 19671001) and the National Centre for Energy and Environment, University of Benin.

8.00E-03 3.00E-04 8.00E-03 5.00E-04

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