Health risk assessment of Ubeji Creek residents’ exposure to BTEX from consumption of locally sourced foods

Figures & data

Figure 1. Relative contribution of foods to the total dietary BTEX intake

Table 1. Instrument settings for the HP 5890 Series II GC and Headspace optimised for BTEX analysis

	Parameter	Setting
GC	Gas Chromatograph	Hewlett Packard Model HP 5890 Series II
	Detector	Agilent FID
	Column	J&W DB-624, 30 m, 0.53 mm ID x 3.0 μm film thickness
	Inlet Mode	Split
	Inlet Temperature	50°C
	Detector Temperature	300°C
	Carrier Gas	Nitrogen, 30 cm^3/sec
	Oven Program	35°C, hold 5 mins, 7°C/min to 120°C
	Total Cycle Time	12 minutes
Headspace	Headspace Auto-sampler	Hewlett Packard Model HP 7694
	Equilibration Time	10 minutes
	Loop Temperature	120°C
	Transfer Line Temperature	120°C
	Headspace Oven	80°C
	Vial Pressure	14 psig
	Vial Pressurization	30 secs

Table 2. Recovery analysis for BTEX determination in biota

Food Sample	Original Sample Conc. (mg/kg)	Weight of Sample Spiked (kg)	Conc. of Standard Spiked (mg/kg)	Increased Conc. Achieved (mg/kg)	Total Conc. Expected by Analysis (mg/kg)	Result of re-analysis (mg/kg)	% Recovery
Fish	0.058	0.1	0.168	1.68	1.738	1.57	90%
Shrimps	0.204	0.1	0.168	1.68	1.884	1.727	91%
Cassava	0.042	0.1	0.168	1.68	1.722	1.536	89%
Pawpaw	0.079	0.1	0.168	1.68	1.759	1.869	107%

Table 3. Summary of assumptions for THQ calculation in this study

Parameter	Description	Value	Unit	Reference
CEXP	Analyte Concentration	Table 4	mg/kg	(Current Study)
FIR	Food Intake Rate	Table 5	kg/person/day	(Current Study)
ED	Exposure Duration	365 days/yr. for 70 yrs.	days	[32,33]
BW	Average Body Weight	67.5	kg	(Current Study)
LT	Life time of exposure	55 years life expectancy age for Nigeria	days	[34]
RfDo	Oral reference dose	BTEX – 0.004, 0.08, 0.1 and 0.2	mg/kg bw/day	[37]

Table 4. The BTEX concentration (mg/kg) of biota samples

	Site Code	n = 5	Benzene	Toluene	Ethylbenzene	m + p-Xylene	o-Xylene	BTEX
Fish	SP3/4	Mean	0.207 ± 0.193	0.099 ± 0.075	0.014 ± 0.013	0.036 ± 0.031	0.015 ± 0.013	0.37 ± 0.32
		Range	<0.001–0.488	<0.001–0.221	<0.001–0.036	<0.001–0.080	<0.001–0.031	<0.001–0.856
Shrimps	SP3/4	Mean	0.199 ± 0.274	0.108 ± 0.113	0.020 ± 0.020	0.045 ± 0.046	0.019 ± 0.019	0.39 ± 0.46
		Range	<0.001–0.697	<0.001–0.312	<0.001–0.053	<0.001–0.129	<0.001–0.052	<0.001–1.243
Pawpaw	SP5	Mean	0.044 ± 0.071	0.081 ± 0.083	0.249 ± 0.410	0.137 ± 0.201	0.051 ± 0.070	0.56 ± 0.74
		Range	<0.001–0.166	<0.001–0.208	<0.001–0.958	<0.001–0.483	<0.001–0.172	<0.001–1.823
Bitter Leaf	SP5	Mean	0.004 ± 0.005	0.055 ± 0.077	0.236 ± 0.333	0.119 ± 0.165	0.044 ± 0.054	0.46 ± 0.63
		Range	<0.001–0.011	<0.001–0.164	<0.001–0.707	<0.001–0.352	<0.001–0.121	<0.001–1.355
Cassava (Tuber)	SP5	Mean	0.062 ± 0.078	0.083 ± 0.055	0.014 ± 0.007	0.044 ± 0.025	0.020 ± 0.012	0.22 ± 0.16
		Range	<0.001–0.173	0.010–0.142	0.004–0.020	0.010–0.065	0.004–0.032	0.042–0.425
Pineapple (Peel)	SP6	Mean	0.063 ± 0.084	0.148 ± 0.086	0.201 ± 0.304	0.133 ± 0.136	0.057 ± 0.048	0.60 ± 0.49
		Range	<0.001–0.189	<0.001–0.269	<0.001–0.773	<0.001–0.386	<0.001–0.141	<0.001–1.490
Pineapple (Tissue)	SP6	Mean	0.896 ± 1.240	0.095 ± 0.070	0.196 ± 0.306	0.119 ± 0.144	0.045 ± 0.050	1.35 ± 0.11
		Range	0.003–3.035	0.022–0.178	0.003–0.726	<0.001–0.363	<0.001–0.129	0.113–4.431

Table 5. THQ and EDI^b of BTEX from consumption of contaminated foods in Ubeji Creek

Food	Benzene		Toluene		Ethylbenzene		Xylene		BTEX
	THQ	EDI	THQ	EDI	THQ	EDI	THQ	EDI	THQ	EDI
Fish	0.0018	0.00038	0.000043	0.00018	0.0000049	0.000026	0.0000089	0.000095	0.0019	0.00069
Shrimps	0.0013	0.00028	0.000036	0.00015	0.0000053	0.000028	0.0000086	0.000091	0.0014	0.00056
Pawpaw	0.000063	0.000013	0.0000058	0.000025	0.000014	0.000076	0.0000054	0.000058	0.000089	0.00017
Bitter Leaf	0.0000074	0.000016	0.0000051	0.000022	0.000017	0.000093	0.0000060	0.000064	0.000036	0.00019
Cassava	0.00011	0.000023	0.0000072	0.000030	0.00000097	0.0000051	0.0000022	0.000023	0.00012	0.000082
Pineapple	0.00078	0.00017	0.0000041	0.000018	0.0000068	0.000036	0.0000028	0.000032	0.00079	0.00025
Total^a	0.00095	0.00087	0.0000098	0.00043	0.0000152	0.00026	0.0000014	0.00036		0.00193
Oral TDI	0.005		0.223		0.0971		0.179

TDI: Tolerable Daily Intake [35,36]

^aAll food combined

^bEstimated Daily Intake in mg/kg/person/day

Table 6. Estimated daily usual food intakes for Ubeji Creek population

Foods			Food Consumption (kg/kg bw/day)
	Mean ± SD	P50	P95	P99	Min – Max	Number of Consumers
Fish	0.0019 ± 0.0073	0.00178	0.0032	0.0036	0.0001–0.0037	530
Shrimps	0.0014 ± 0.0007	0.00127	0.0027	0.0036	0.0000–0.0036	485
Pawpaw	0.0003 ± 0.0002	0.000227	0.0007	0.0008	0.0000–0.0008	510
Bitter Leaf	0.0004 ± 0.0002	0.000308	0.0009	0.0010	0.0000–0.0011	525
Cassava	0.0004 ± 0.0020	0.000333	0.0008	0.0009	0.0000–0.0010	490
Pineapple	0.0002 ± 0.0002	0.00015	0.0007	0.0008	0.0000–0.0008	315
Total^a	0.0045 ± 0.0013	0.0044	0.0065	0.0074	0.0010–0.0080	275

^aAll food combined

Table 7. Deterministic analysis results of dietary BTEX intake (mg/kg bw/day)

Foods	BTEX Intake (mg/kg bw/day)
	Mean ± SD		P50	P95	P99		Min – Max
Fish	0.0007 ± 0.0003		0.0007	0.0012	0.0013		0.0002–0.0014
Shrimps	0.0006 ± 0.0003		0.0005	0.0010	0.0014		0.0000–0.0014
Pawpaw	0.0002 ± 0.0001		0.0001	0.0004	0.0004		0.0000–0.0005
Bitter Leaf	0.0002 ± 0.0001		0.0001	0.0004	0.0005		0.0000–0.0005
Cassava	0.0001 ± 0.00004		0.0001	0.0002	0.0002		0.0000–0.0002
Pineapple	0.0002 ± 0.0003		0.0002	0.0009	0.0010		0.0000–0.0011
Total^a	0.0019 ± 0.0007		0.0018	0.0031	0.0035		0.0004–0.0037

^aAll food combined

Table 8. Deterministic analysis results of dietary benzene intake (mg/kg bw/day)

Foods	Benzene Intake (mg/kg bw/day)
	Mean± SD		P50	P95	P99		Min – Max
Fish	0.0004 ± 0.0002		0.0004	0.001	0.0008		0.0001–0.001
Shrimps	0.0004 ± 0.0001		0.0003	0.001	0.0007		0.000–0.001
Pawpaw	0.00001 ± 0.000001		0.00001	0.00003	0.00003		0.000–0.00004
Bitter Leaf	0.00002 ± 0.0000001		0.000001	0.000003	0.000004		0.000–0.000004
Cassava	0.00002 ± 0.00001		0.00002	0.0001	0.000006		0.000–0.0001
Pineapple	0.0002 ± 0.0002		0.0001	0.001	0.0007		0.000–0.001
Total^a	0.001 ± 0.0003		0.01	0.001	0.002		0.0002–0.002

^aAll foods combined; Benzene: RfDo = 0.0040; MRL = 0.0050; MPR = 0.0033

Figure 2. Probabilistic distribution graph (A) and P-P plot (B) of all foods combined

Figure 3. Probabilistic distribution graph (A) and P-P plot (B) of benzene distribution in all analysed foods

Figure 4. Probabilistic distribution graph (A) and P-P plot (B) of BTEX distribution in all analysed food

Table 9. Probabilistic analysis results of food consumption (kg/kg bw/day)

Foods	Food Consumption (kg/kg bw/day)					Number of Consumers
	Mean± SD		P50	P95	P99
Fish	0.0019 ± 0.00073		0.0018	0.0032	0.0036	530
Shrimps	0.0013 ± 0.00078		0.0013	0.0025	0.0034	485
Total^a	0.0045 ± 0.0013		0.0045	0.0067	0.0076	275

^aAll foods combined

Table 10. Probabilistic analysis results of dietary benzene intake (mg/kg bw/day)

Foods	Benzene Intake (mg/kg bw/day)
	Mean± SD		P50	P95	P99
Fish	0.00031 ± 0.00015		0.00018	0.0019	0.0031
Shrimps	0.00020 ± 0.00015		0.00012	0.0014	0.0030
Total^a	0.0010 ± 0.00032		0.00071	0.0047	0.0083

^aAll foods combined

Table 11. Probabilistic analysis results of dietary BTEX intake (mg/kg bw/day)

Foods	BTEX Intake (mg/kg bw/day)
	Mean± SD		P50	P95	P99
Fish	0.00056 ± 0.00027		0.00032	0.0033	0.0059
Shrimps	0.00040 ± 0.00030		0.00025	0.0028	0.0059
Total^a	0.0221 ± 0.000		0.00061	0.0154	0.0869

^aAll foods combined

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