J of IMAB. 2018 Apr-Jun;24(2) https://www.journal-imab-bg.org 2069

ABSTRACTChronic neurotoxicity of lead is a major problem in

all countries around the world. Long-term exposure to leadin the environment has recently become of interest as apossible risk factor for cognitive impairment in theinvolved workers. The consequences for the brain aftercessation of the exposure are also subject to research.

Our study aimed at investigating and analyzing thecognitive impairment in workers in professional contactwith lead.

Seventy-two men in chronic professional contactwith lead aerosols were examined. They were aged 39.4 ±10.4 (19 - 58) years, their average duration of service was13.0 ± 8.7 (1 - 33) years, and the mean blood leadconcentration was 43.4 ± 9.0 µg/dl. The screening setincluded a subjective cognitive impairment questionnaire,a depression scale, a set of cognitive tests (MMSE, IST,DRT, CDT), and a scale for activities of daily living (4-IADLScore).

With the increase of blood lead levels, a statisticallyreliable trend was observed for decrease of MMSE, IST andCDT scores. Mild cognitive impairment manifesting withdisturbance of construction praxis, planning, short-termmemory and concentration could probably be related to thetoxic effects of lead.

Keywords: blood lead level, professional exposureto lead, cognitive impairment

INTRODUCTIONIn recent years, there has been a number of

publications discussing the cumulative lead (Pb) dose andthe concentration of lead in blood. Data on the relationshipwith cognitive disturbances are also available.Nevertheless, the threshold for adverse effects on humanhealth and the role of lifetime exposure as a factor forchronic disease are yet to be clarified [1]. The association

between lead concentration in blood and cognitivefunctioning is considered more apparent in professionalgroups with high lead exposure, but the relationshipbetween bone lead levels and the decline in cognitivefunction is stronger in studies of older individuals withlower blood lead concentration [2, 3, 4].

The recommendation of the World HealthOrganization for adults is to maintain the blood leadconcentration below 10 µg/dL. Some studies demonstratedcognitive impairment in workers with blood leadconcentration of 20-40 µg/dL. There is no “safe” threshold,but blood lead levels below 5 µg/dL are known not toincrease short- and long-term risk and to require no furthermanagement [5]. Nevertheless, even a low level of lead mayhave a negative impact on cognitive function. Long-termcumulative lead exposure may be associated with fastercognitive decline and with accelerated cognitive aging [6-11]. A decrease of Mini-Mental State Exam (MMSE) score<24 with increase of the levels of lead in blood and patellahas been reported. High levels of lead in the patella maycorrespond to approximately 5 years of aging relative tothe baseline MMSE score [12]. Low-level cumulativeexposure to lead may adversely the visuospatial/visuomotor domain of cognition [13]. Cognitiveimpairment in chronic lead exposure may be regarded as asubclinical symptom of CNS damage.

MMSE is a well-known neuropsychologicalinstrument [14]. If used for screening, a combinedadministration with other tests is recommended in order toincrease the sensitivity and reliability of the study. TheClock Drawing Test (CDT) [15] is considered suitable forthe purpose.

The aim of the present study is to assess cognitiveimpairment in workers in professional contact with lead.

PATIENTS AND METHODS:For the purpose of the study, 72 workers in chronic

Original article

OCCUPATIONAL LEAD EXPOSURE ANDCOGNITION IN ADULTS

Veselinka Nestorova1, Borislav Ivanov2, Iskra Mircheva3, Ivan Dimitrov4, AraKaprelyan5, Kalina Drenska5

1) Department of Physiotherapy, rehabilitation, thalassotherapy, occupationaldiseases, Faculty of Public Health, Medical University, Varna, Bulgaria.2) Department of clinical medical sciences, Faculty of Dental Medicine, MedicalUniversity, Varna, Bulgaria.3) Department of social medicine and healthcare organization, Faculty ofPublic Health, Medical University, Varna, Bulgaria.4) Department of nursing, Sliven affiliate, Medical University, Varna, Bulgaria.5) Department of Neurology and neuroscience, Faculty of Medicine, MedicalUniversity, Varna, Bulgaria.

Journal of IMAB - Annual Proceeding (Scientific Papers). 2018 Apr-Jun;24(2)Journal of IMABISSN: 1312-773Xhttps://www.journal-imab-bg.org

https://doi.org/10.5272/jimab.2018242.2069

2070 https://www.journal-imab-bg.org J of IMAB. 2018 Apr-Jun;24(2)

professional contact with lead aerosols were examined.They had an average age of 39.4 ± 10.4 (19 - 58) years, anaverage length of service of 13.0 ± 8.7 (1 - 33) years, andmean lead concentration in blood of 43.4 ± 9.0 µg/dl.

The surveyed workers were divided into four agegroups: up to 30 years, 30 to 40 years; 40 to 50 years, andover 50 years.

According to the duration of the exposure, thepersons were divided into five groups: up to 5 years - 17subjects; up to 10 years - 12; up to 15 years - 13; up to 20years. – 17, and over 20 years - 13.

They were also grouped according to blood leadlevels: below 40 µg/dl; 40-50 µg/dl; 50-60 µg/dl; 60-70µg/dl, and above 70 µg/dl.

History of harmful habits, accompanying diseasesand memory disorders was taken.

Neuropsychological testing was performed in allsubjects. The Mini-Mental State Examination (MMSE),Isaacs Set Test (IST), Digit Repetition Test (DRT) and ClockDrawing Test (CDT) were applied. The 4-IADL score wasused to look for impairment of the activities of daily living.All neuropsychological tests were performed in accordancewith generally accepted requirements and rules. Theassessment was made in line with the individual conditionof the investigated person.

Study data were organized in MS Excel, and SPSS12 software was used for analysis.

All surveyed persons gave informed consent for thesurvey.

RESULTS:EducationWorkers with specialized secondary education were

predominant (n=24, 33.3%). Those with secondaryeducation were 22 (30.55%), 22 (30.55%) had primaryeducation, and 4 (5.56%) of the surveyed subjects hadstudied for 7 years.

Medical HistoryTwenty-four (33.3%) of the workers reported

hypertension, 6 (8.33%) - nephrolithiasis, and 1 (1.38%) -diabetes mellitus. Non-smokers were 24 (33.3%) of thesurveyed.

Subjective good health was reported by 36participants (50%), very good - 20 (27.78%), average - 14(19.45%) and poor – by 2 (2.76) workers.

Questionnaire for subjective cognitive disordersWe conducted a survey of subjective cognitive

impairment in all subjects. All respondents answered “No”to the questions asked, i.e. they did not report subjectivecognitive impairment.

Mini Mental State Examination (MMSE)The most common score was 28 points in 22% (n =

16) of subjects, followed by 29 points - 13.89% (n = 10),and 30 points - 11.11% (n = 8). Positively screened personsaccording to MMSE with less than 24 points were 15.28%(n = 11), and those with less than 27 points were 37.28%(n = 27) (Figure 1).

Fig. 1. Distribution of MMSE results according to the number of persons screened

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A statistically significant relationship between theage of the studied subjects and MMSE was found (p =0.01), as well as between the exposure period and MMSE(p = 0.001). A statistically significant correlation wasobserved between blood lead levels and MMSE (p =0.001).

With the increase of lead in blood, MMSE score wasdecreasing significantly (p = 0.001).

Of the positively screened individuals, 5 (6.95%)had blood lead values from 40 µg/dl to 50 µg/dl. Therewere no positively screened persons with blood leadconcentration below 40 µg/dl.

Isaacs Set Test for verbal fluency (IST)The most common result was 39 points (11.11%, n

= 8), followed by 38 in 9.72% (n = 8), and 35 in 9.72% (n= 8) of the surveyed persons. There was a significantcorrelation between blood lead levels and IST score (p =0.001).

With the increase of blood lead levels, the achievedIST score was reduced (p = 0.001).

Digit Repetition Test (DRT)The most common result was the maximal – 10

points in 22.22% (n = 16) of the surveyed subjects. Therewas a significant relationship between blood lead levelsand DRT score (p = 0.001). A correlation was found betweenage and DRT (p = 0.007), as well as between the durationof exposure and DRT (p = 0.027).

With the increase of blood lead levels, DRT scorewas reduced (p = 0.001).

Seven individuals (9.72%) were positively screenedwith blood lead concentration between 40 µg/dl and 50 µg/dl.

Eleven screened subjects (15.28%) achieved a scoreof <7 points, which identified them as positively screenedaccording to DRT (Figure 2).

Fig. 2. Distribution of DRT results by number of screened individuals

Clock Drawing Test (CDT)The most common score was 9 points in 27.28% (n

= 20) of the surveyed subjects.With the increase of lead in blood, the achieved CDT

score (p = 0.001) was reduced.Only one positively screened subject had a blood

lead concentration below 40 µg/dl, while 11 hadconcentrations between 40 µg/dl and 50 µg/dl.

Nineteen screened individuals (26.39%) achieved ascore of <7, which identified them as positively screenedaccording to CDT (Figure 3).

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Fig. 3. Distribution of CDT results according to the number of individuals screened

DISCUSSION:Mean values of MMSE, IST, DRT and CDT scores

show a statistically significant tendency for a decrease withthe increase of blood lead concentration.

MMSEThe relative share of positive screened persons

through MMSE is high (15.28%). The MMSE test includescomponents which explore different cognitive domains,such as orientation to time and place, memory, attention,calculation, speech, gnosis, and praxis. There is asignificant correlation between blood lead levels andMMSE, which coincides with the data of Weisskopf et al.[13].

ISTThe test characterizes speech output and semantic

memory. All patients achieved a score of >20 points whichdoes not classify them as positively screened. This isconsistent with literature data. Higher blood lead levels areassociated with lower IST score.

Digit Repetition Test (DRT)The test examines primarily short-term memory,

concentration, and focusing ability. The data reveal acorrelation between age and DRT score, as well as betweenthe duration of the exposure and DRT. Higher blood leadlevels are associated with lower DRT score.

Clock Drawing Test (CDT)Nineteen screened persons (26.39%) achieved a

score of <7, classifying them as positively screenedaccording to CDT.

The distribution of surveyed workers by agerevealed that there were no workers over 60 years of age.Specialized secondary and secondary education werepredominant among the surveyed subjects. Advanced ageand low level of education below 6 years are risk factorsfor cognitive impairment, and there are coefficients forcorrecting the results of cognitive tests accordingly.

CONCLUSIONS:Our study found a lack of depressive symptoms and

subjective cognitive complaints. The assessed persons hadno evidence of severe cognitive impairment. Mostpositively screened subjects were detected using CDT(26.39%), followed by MMSE (15.28%), and DRT(15.28%). The greater part of positively screened workershad blood lead concentration between 40 µg/dl and 50 µg/dl.

Possible mild cognitive impairment manifestingwith disturbance of construction praxis, planning, short-term memory and concentration could probably beattributed to the toxic effects of lead and has a potentialto be a subclinical marker.

Acknowledgement:There was no funding source for this study. All

authors had full access to all the study data. Thecorresponding author had final responsibility for thedecision to submit for publication.

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Address for correspondence:Veselinka Nestorova,Department of Physiotherapy, rehabilitation, thalassotherapy, occupationaldiseases, Medical University, Varna, 55, Marin Drinov str., 9002 Varna, Bulgaria.E-mail: dr_nestorova@yahoo.de

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Please cite this article as: Nestorova V, Ivanov B, Mircheva I, Dimitrov I, Kaprelyan A, Drenska K. Occupational LeadExposure and Cognition in Adults. J of IMAB. 2018 Apr-Jun;24(2):2069-2073.DOI: https://doi.org/10.5272/jimab.2018242.2069

Received: 08/05/2018; Published online: 21/06/2018