Effect of Rinsing Canned Foods on Bisphenol-A Exposure: The Hummus Experiment

Abstract

Bisphenol-A (BPA) is associated with adverse health outcomes and is found in many canned foods. It is not understood if some BPA contamination can be washed away by rinsing. The objective of this single-blinded crossover experiment was to determine whether BPA exposure, as measured by urinary concentrations, could be decreased by rinsing canned beans prior to consumption. Three types of hummus were prepared from dried beans, rinsed, and unrinsed canned beans. Fourteen healthy participants ate two samples of each hummus over six experimental days and collected spot urine specimens for BPA measurement. The geometric mean BPA levels for dried beans BPA (GM = 0.97 ng/ml, 95%CI = 0.74,1.26) was significantly lower than rinsed (GM = 1.89 ng/ml, 1.37,2.59) and unrinsed (GM = 2.46 ng/ml, 1.44,4.19). Difference-in-difference estimates showed an increase in GM BPA from pre- to post-hummus between unrinsed and rinsed canned beans of 1.39 ng/ml, p-value = 0.0400. Rinsing canned beans was an effective method to reduce BPA exposure.

Introduction

Bisphenol A (BPA)—a common chemical used in polycarbonate plastics and epoxy resins frequently used to store food and water (e.g., water bottles, dental sealants, canned foods, bottle caps)—is a known endocrine disruptor. BPA exposure has been associated with impaired reproductive health outcomes including immune dysfunction (Clayton et al., 2011), fertilization implantation failure (Ehrlich et al., 2012), male sexual dysfunction, and altered hormone levels and reduced sperm quality in males (Meeker et al., 2011). Other health outcomes such as hormone-associated cancers (H. Gao et al., 2015), cardiovascular diseases (X. Gao & Wang, 2014), diabetes (Sun et al., 2014), and asthma (Kim et al., 2014) have also been associated with BPA, but are less established.

A small but innovative crossover study at Harvard University randomly assigned participants to eat fresh soup for lunch daily for five consecutive days and canned soup for five consecutive days (order of soup was blinded) (Carwile et al., 2011). Urinary BPA concentration were over 1,000% higher during the canned soup ingestion week compared to the same individual’s fresh soup consumption week, demonstrating the impact of transient BPA exposures to commercially available foods on concentrations measured in human subjects (Carwile et al., 2011).

Objective

It is well established that canned goods are a common source of BPA. However, it is not understood if some BPA contamination can be washed away by rinsing the food prior to ingestion. We performed a single-blinded crossover experiment to determine whether BPA exposure, as measured by urinary concentrations, could be decreased by rinsing canned beans prior to consumption. Because of the quick metabolism of BPA (half-life ~6 hours), it is reasonable to expect daily variation in measures of exposure and therefore collect samples over multiple days at multiple times of the day (Volkel et al., 2002).

Methods

Healthy male and female adult volunteers were recruited from among faculty, staff, and students affiliated with The University of Utah Department of Family and Preventive Medicine for this pilot-scale study; participants had no known health issues that would affect BPA consumption or metabolism. Volunteers agreed to consume portions of hummus two times a week for three weeks and to provide urine samples in the morning and afternoon on each of 6 experimental days during the 3-week duration of the study. Hummus was prepared by the same local restaurant for each experimental condition: prepared from dry beans, canned beans that were drained but not rinsed, and canned beans that were drained and rinsed three times for one minute each. Each participant was given one, two-ounce sample of hummus on two consecutive days in a week followed by a washout period of 4–6 days (Figure 1). This was done for all three hummus types.

Figure 1. Study protocol for crossover hummus consumption.

Total BPA was measured in the urine samples using ultra-high-performance liquid chromatography–tandem mass spectrometry (Anderson et al., 2014). In statistical analysis, clustered generalized estimating equations (GEE) with gamma distribution and log link were used to account for three types of hummus with both pre- and post-exposure BPA measurements and multiple measurements per person. The GEE models included indicators for time (pre- or post-hummus), hummus type, and an interaction term between these variables. All models were adjusted for age and sex.

Results

A total of 14 participants were enrolled, including 10 females and 4 males with a mean age of 28.9. +/− 6.3 years (Table 1).

Table 1. Demographics of study population.

There were 161 samples collected of the 168 expected (95.8% compliance). Table 2 shows BPA concentrations by age and sex.

Table 2. Geometric mean BPA concentrations (ng/mL) by demographic characteristics.

LLOQ = lower limit of quantitation (0.75 ng/ml) GM = geometric mean, BPA = Bisphenol A.

Figure 2 shows the BPA GM for pre- and post-hummus samples by hummus type. There were no significant differences in the BPA GM pre-hummus. The BPA GM post-hummus with dried beans (GM = 0.97 ng/ml, 95% CI = 0.74, 1.26) was significantly lower than the post-hummus measurements for the rinsed canned beans (GM = 1.89 ng/ml, 95% CI = 1.37, 2.59) and the unrinsed canned beans (GM = 2.46 ng/ml, 95% CI = 1.44, 4.19).

Figure 2. Geometric mean BPA pre- and post-consumption of each hummus type.

As shown in Table 3, both types of canned beans, had significantly increased BPA from the pre- to post-hummus conditions. We did not see a significant increase from pre- to post-hummus with the dried beans (β = 0.04 ng/ml, p-value = 0.8628). Correspondingly, the DD estimates showed a 1.4 ng/ml increase in BPA from pre- to post-hummus between unrinsed canned beans and rinsed canned beans (p-value = 0.0400).

Table 3. Model estimates from pre- vs post-hummus eating and difference-in-difference results.

DD = difference-in-difference.

* Adjusted for age and sex.

Discussion

Our results matched the hypothesis of a dose–response increase in BPA from dry beans to rinsed canned beans to unrinsed canned beans and highlights rinsing as one potential way for individuals to reduce BPA exposure. As BPA has been associated with many adverse reproductive effects (Clayton et al., 2011; Ehrlich et al., 2012; Tomza-Marciniak et al., 2018), consumers seek to minimize exposure especially during childhood and reproductive years. While rinsing the beans did not remove all BPA exposure, in adjusted models the estimate from pre- to post-hummus was nearly three (2.88) times lower in the rinsed canned beans compared to the canned beans that were drained but not rinsed.

Conclusions

It has been well established that consumption of canned foods is associated with increased urinary BPA concentrations (Carwile et al., 2011; Hartle et al., 2016). Further, canned fruits and vegetables (which includes beans) have been reported to be among the canned foods with the highest BPA concentrations along with soups and pasta (Hartle et al., 2016). While it may not be possible to rinse all canned foods, this method has been shown to be effective in our pilot study. This is a cost-effective method that consumers can easily use to reduce BPA exposure. Future studies are needed to examine this with a larger sample size and across other canned foods.